JP4551806B2 - Zirconia green sheet, zirconia sheet and production method thereof - Google Patents

Description

  The present invention relates to a zirconia-based green sheet, a zirconia-based sheet, and a method for producing the same, and more specifically, a dense body having a density of 98% or more with respect to a theoretical density, as a solid electrolyte membrane used for a fuel cell, a sensor, or the like. The present invention relates to a useful zirconia-based sheet, a zirconia-based green sheet which is a precursor for obtaining the sheet, and a method for producing the same.

Zirconia-based sheets used as solid electrolyte membranes for fuel cells, oxygen sensors, etc. are desirably dense in order to enhance their suitability for use, and many studies from such viewpoints have already been published. . For example, Patent Document 1 discloses a ceramic sheet having a thickness of 0.05 to 0.6 mm, a thickness unevenness of an arbitrary 400 cm ² region within 5%, and a density of 95% or more of the theoretical density. In addition, as a ceramic green sheet to be a precursor for obtaining the ceramic sheet, a green sheet composed of ceramic powder and an organic binder, the average diameter of pores present in the sheet is 100 to 1000 nm, and A green sheet having a total pore volume of 0.02 to 0.2 cc / g is disclosed.

  According to Patent Document 1, if the pore size in the green sheet is less than 100 nm, the powder is too clogged and solvent removal or degreasing becomes insufficient. On the other hand, if the pore size exceeds 1000 nm, the distance between the powders becomes large. If the total pore volume of the green sheet is less than 0.02 cc / g, the powder becomes too clogged and solvent removal or degreasing becomes insufficient. When the total volume of the pores exceeds 0.2 cc / g, it has been pointed out as a problem that a portion where the distance between the powders is too large is formed, the sheet strength is lowered, and handling becomes difficult.

However, according to the example of Patent Document 1, the green sheet with the pore diameter and the total pore volume defined is formed by a doctor blade method using a slurry prepared by a 2 L (liter) ball mill. The ceramic sheet obtained by firing this green sheet tends to have a large strength variation. From the results of the study by the present inventors, such a tendency is 11 or more in the region where the number of closed pores observed by taking a photograph of the longitudinal section of the sheet with a 408 nm laser light microscope is 90 × 65 μm ² , It is also expressed when the Weibull coefficient is 10 or less.

Patent Document 2 discloses a zirconia sintered body containing magnesia in a range of 7 to 9 mol% and having 5 or less pores having a diameter of 1 μm or more on the surface per 1000 μm ² . The pores mentioned here are those in which the surface of the sintered body is ground or cut and cut to a depth of about 5 mm, and when this is mirror-polished, the surface is observed as black with a diameter of 1 μm or more when observed with an electron microscope. . The amount of pores is an average of 1000 μm ² measurement surfaces taken from the photographed photographs, and the number of pores with a diameter of 1 μm or more present in them is measured at 10 arbitrary locations. is there.

  However, this technique forms the raw material powder by die molding, rubber press, injection molding, and extrusion molding, and does not describe the cause of the occurrence of pores in the obtained zirconia sintered body, as in the present invention. This is completely different from the zirconia sheet produced by the doctor blade method.

On the other hand, Non-Patent Document 1 describes that void defects generated in a green sheet can be greatly reduced by defoaming a slurry used for sheet forming. The defoaming time and per 1 dm ² in the green sheet are described. The relationship between the number of voids is shown. However, the relationship between the average diameter of pores existing in the green sheet and the pore volume ratio has not been clarified.

Further, Non-Patent Document 2 describes that the coating slurry is laid or defoamed in order to suppress heat and air bubbles generated in the mixing and dispersing step using a ball mill or a bead mill in the coating slurry preparation step. . However, it is not disclosed to reduce the porosity by stirring the slurry adjusted to a predetermined viscosity while defoaming under specific conditions.
JP-A-10-212166 Japanese Patent Laid-Open No. 6-40769 “Fine ceramics molding and organic materials” (Katsuyoshi Saito, CMC Co., Ltd., August 26, 1985, pp. 237-238) "Development of multilayer ceramic capacitor, material technology and high reliability", Technical Information Association, Inc., February 28, 2001, pp. 103-104

The present invention has been made for further improvement of the conventional technology as described above. Specifically, for example, closed pores observed by taking a photograph of a longitudinal section of a sheet with a 408 nm laser light microscope. Zirconia with a stable quality with less unevenness in strength, with a low value of 10 or less in the area of 90 × 65 μm ² , excellent fracture toughness, and a Weibull coefficient of bending strength of 10 or more To provide a dense green sheet with less internal void defects, which is a precursor of such a zirconia-based sheet, and to stably produce such a green sheet with high productivity. It is to provide a method that can.

  The green sheet according to the present invention that has solved the above problems is a zirconia-based green sheet that is formed by a doctor blade method and includes a zirconia-based powder and a binder, and is measured by a mercury intrusion method. The average pore diameter of pores present therein is 0.01 to 0.08 μm, and the total pore volume is 0.01 to 0.05 mL / g.

Particularly preferred as the zirconia-based powder used in the present invention is a content of 3 to 12 mol% with respect to zirconia as a stabilizer containing at least one oxide selected from the group consisting of scandium oxide, yttrium oxide and ytterbium oxide. It is desirable that the powder has a specific surface area of 3 to ²⁰ m ² / g.

The zirconia-based sheet of the present invention is a high-density zirconia-based material useful as a solid electrolyte membrane for fuel cells, sensors, etc., obtained by firing a zirconia-based green sheet that meets the above specified requirements at 1300 to 1500 ° C. a sheet, the sheet thickness at 50～800Myuemu, the number of closed pores observed by photographing a longitudinal section of the sheet with a laser beam microscope 408nm is 90 × 65μm ² (i.e. 5850μm ²⁾ regions It is characterized in that it is 10 or less.

Furthermore, the production method of the present invention is positioned as a method capable of industrially producing a zirconia-based green sheet having the above-mentioned characteristics stably with high productivity.
[A] A milling step of milling a raw material containing a zirconia-based powder, a binder and a solvent to obtain a slurry having a viscosity of 1.5 Pa · s or less,
[B] The slurry was removed under reduced pressure so that the viscosity at 20 ° C. was in the range of 2.7 to 6.7 Pa · s in a vessel equipped with stirring blades, and the solid content concentration was 50 to 85% by mass. A vacuum stirring step to obtain a slurry,
[C] Stirring the resulting slurry with stirring blades immersed in the slurry at room temperature and normal pressure, stirring power: 1.5 to 2.5 kW / m ³ , rotation speed: 5 to 20 rpm, and stirring for 1 to 50 hours Process,
[D] Then, the stationary process of leaving still for 10 minutes-25 hours, without rotating a stirring blade,
There is a gist where the slurry obtained by the above method is used and the sheet is formed by the doctor blade method.

  The zirconia green sheet of the present invention has an average pore diameter of 0.01 to 0.08 μm and a total pore volume of 0.01 to 0.05 mL in the green sheet measured by the mercury intrusion method. By specifying in the range of / g, decomposition and combustion gas generated during firing can be efficiently released to the outside of the sheet and sintering can be carried out efficiently, and there are no pore defects, etc., and high-density, homogeneous and excellent physical properties The zirconia-type sheet | seat which has can be obtained. And according to the manufacturing method of this invention, the green sheet used as the precursor which gives the zirconia-type sheet | seat of the outstanding performance as mentioned above can be obtained reliably with sufficient productivity.

  The green sheet of the present invention is a precursor of a ceramic sheet used as a solid electrolyte membrane for a fuel cell or a sensor as described above, and contains a zirconia-based powder and a binder, and is formed by a doctor blade method. Paying attention to the size and volume ratio of the pores present in the green sheet measured by the mercury intrusion method, the average pore diameter of the pores is in the range of 0.01 to 0.08 μm. In addition to solving the above-mentioned problems that could not be solved by the prior art by setting the total pore volume in the range of 0.01 to 0.05 mL / g, the reason for setting these requirements is It is as follows.

  Organic components such as binders and plasticizers and dispersants contained in the green sheet, which is a precursor of the zirconia-based sheet, are oxidized when the green sheet is baked, and carbon dioxide gas, water, etc. Decomposition gas and organic component decomposition / combustion gas are generated and released to the outside of the seat. However, these gases are not diffused out of the green sheet and are confined in the green sheet unless the green sheet has appropriate pores communicating with the outside. This trapped gas expands in volume due to further temperature rise, and causes void defects such as blisters and holes on the surface of the green sheet, which deteriorates the surface properties and flatness of the ceramic sheet and reduces the strength. Cause. Further, if the decomposition gas or the like is confined in the green sheet without being released during firing, and finally remains as closed pores in the zirconia-based sheet, it causes a decrease in density and strength.

  In order to avoid such a problem, the pores (holes) remaining in the zirconia-based sheet must be further refined and reduced in number as compared with the pores disclosed in the aforementioned Patent Document 1 and the like. For that purpose, it is effective to have appropriate pores in the green sheet as long as the strength, density and flatness of the green sheet as a precursor are not lowered. From such a viewpoint, in the present invention, the average pore diameter and the total pore volume of the pores existing in the green sheet are defined as follows.

Average pore diameter: 0.01 to 0.08 μm
In the green sheet having an average pore diameter within the above-mentioned preferred range, not only the decomposition gas and combustion gas generated during firing are smoothly diffused out of the sheet, but also the pores shrink during sintering and further refined, or It becomes easy to disappear, and the obtained sintered body (that is, zirconia-based sheet) becomes a high-density dense body and has excellent physical properties such as bending strength. By the way, if the average pore diameter is less than 0.01 μm, the release of decomposition gas and combustion gas at the time of firing becomes slow, and not only voids remain in the interior and void defects are easily generated, but also the density of the sintered body However, the physical properties are also deteriorated.

  When the average pore diameter exceeds 0.08 μm, the decomposition gas and combustion gas generated during firing proceeds smoothly, but the pores in the green sheet do not adhere and disappear during sintering (that is, they are crushed) (Not) remain as pores in the ceramic sheet, hindering the increase in sheet density and decreasing the strength. From such a viewpoint, a more preferable value of the average pore diameter is 0.02 μm or more and 0.06 μm or less.

  The average pore diameter mentioned here is a value measured by a mercury intrusion method using an automatic porosimeter “Autopore III9420” manufactured by Micromeritec. The employed mercury pressure was 1 to 60000 psia, and the sample used was a sample having a mass of 2 to 2.3 g obtained by cutting a green sheet into a width of about 10 mm and a length of about 350 mm and winding it in a spring shape. The average pore diameter is a value obtained by dividing the total pore volume by the specific surface area of the pores, assuming that the pores are cylindrical, and this value represents the average diameter of the capillary pore groups. Yes.

Total pore volume: 0.01 to 0.05 mL / g
When the total pore diameter is within the above preferred range, the diffusion of cracked gas and combustion gas to the outside of the sheet proceeds smoothly, and the adhesion / disappearance of the pores during sintering also proceeds rapidly. The sintered body is dense and excellent in physical strength. By the way, if the total pore diameter is less than 0.01 mL / g, the diffusion of cracked gas and combustion gas to the outside of the sheet is delayed, some of them remain as voids in the sheet, and void defects are likely to occur, and the density also decreases. Will tend to. Also, if the total pore volume exceeds 0.05 mL / g, the decomposition gas and combustion gas can be diffused out of the sheet smoothly, but the pores in the sheet cannot be completely adhered and disappeared as pore defects. Not only does it remain, causing a decrease in density, but also the physical strength tends to decrease. From such a viewpoint, the more preferable total pore volume is 0.02 mL / g or more and 0.04 mL / g or less.

  The total pore volume mentioned here is a value measured by the same mercury intrusion method as described above using the same autoporosimeter “Autopore III9420” manufactured by Micromeritec. That is, it is a value obtained by dividing the integrated value of the pore volume into which mercury is injected up to the maximum pressure during measurement by the weight of the sample.

In order to obtain a green sheet satisfying the above average pore diameter and total pore volume by the doctor blade method, bubbles in the raw material slurry are degassed as much as possible to make the pores in the green sheet as small and small as possible. For this purpose, a milling step [A] for obtaining a slurry having a viscosity of 1.5 Pa · s or less by milling a raw material containing a zirconia-based powder as a raw material and a binder, a solvent, and the like, When the viscosity is adjusted while distilling off the solvent in a vessel equipped with stirring blades to obtain a slurry for coating, the solvent is adjusted so that the viscosity at 20 ° C. is in the range of 2.7 to 6.7 Pa · s. A vacuum stirring step [B] for obtaining a slurry having a solid content concentration of 50 to 85 mass% by distilling off under reduced pressure, stirring power of this slurry with stirring blades immersed in the slurry under normal temperature and normal pressure: 1.5 to 2.5k / M ^3, the rotational speed: stirring step of stirring at 1-50 h at 5~20rpm [C], then successively passed through the standing step [D] to 25 hours stand 10 minutes without rotating the stirring blade After that, it is important to perform sheet forming by the doctor blade method.

  That is, in this method, after all of the raw material components are finely dispersed without forming aggregates to form a uniform slurry, bubbles contained in the highly viscous slurry suitable for the doctor blade method are made as much as possible. Therefore, it is an indispensable requirement for controlling the average pore diameter and the total pore volume as a green sheet within the above-mentioned preferable ranges.

  By the way, when the above raw material powder and binder are uniformly dispersed in a solvent by milling, if the viscosity is too high, a part of the solid component aggregates to form a so-called “dama” state, which can be easily performed by subsequent stirring. Since it is difficult to disintegrate and disperse, in order to eliminate such a phenomenon, it is desirable to sufficiently reduce the viscosity when mixing raw material powders into a slurry.

  In addition, when a low-viscosity slurry containing an organic solvent is degassed under reduced pressure, the solvent is volatilized and removed in a boiling state to increase the solid content concentration, resulting in a high-viscosity slurry. It is easy to entrain and the air and dissolved oxygen in the slurry cannot be removed efficiently. In addition, if the highly viscous slurry is only stirred at room temperature and normal pressure, the air and dissolved oxygen present in the slurry will only rotate in the slurry as the stirring blades rotate, raising the bubbles to the liquid level. You cannot degas.

  Therefore, in the present invention, when preparing a slurry for coating by milling a raw material slurry containing a zirconia-based powder, a binder and a solvent using a ball mill, a bead mill or the like, and adjusting the viscosity under reduced pressure in a vessel equipped with a stirring blade. First, in the first milling step [A], a slurry having a viscosity of 1.5 Pa · s or less is prepared by milling the raw material. This step [A] is a step necessary to uniformly disperse the raw materials uniformly. If the viscosity during milling exceeds 1.5 Pa · s, part of the milling step [A] becomes poorly dispersed. In some cases, agglomerates may remain, and the agglomerates remain substantially intact after that, which significantly impairs the coatability of the doctor blade. Therefore, in order to obtain a uniform slurry by uniformly milling the raw materials at this stage, the viscosity at the time of milling should be at most 1.5 Pa · s or less, preferably 1.0 Pa · s or less.

  The lower limit of the viscosity at this time is not particularly limited, but if the viscosity is excessively low, the concentration of the zirconia-based powder becomes low and the amount of the solvent used becomes meaningless, which is uneconomical. Since it takes a long time to volatilize and lower the productivity, it is not practical to reduce the viscosity to less than 0.1 Pa · s. The lower limit of the preferred viscosity is about 0.3 Pa · s.

  The relatively low-viscosity homogeneous slurry obtained in the milling step [A] is charged into a container with a stirring blade in the subsequent reduced pressure stirring step [B], and the viscosity is removed while volatilizing and removing the solvent under reduced pressure. And a slurry having a viscosity at 20 ° C. of 2.7 to 6.7 Pa · s and a solid concentration of 50 to 85 mass% is obtained.

  In addition, solid content concentration here represents the total amount of the raw material powder and binder solid component in all the slurry components in the mass%.

  This step [B] is carried out as a step for efficiently removing the solvent contained in the slurry in a shorter time and efficiently, and the slurry at a temperature of 20 ° C. at the end of the step [B]. When the viscosity is less than 2.7 Pa · s and the solid content concentration is less than 50% by mass, the solvent in the slurry is not yet sufficiently removed, and the amount of the solvent in the slurry is too large and the slurry viscosity is low. The removal of air and dissolved oxygen in the slurry by stirring under normal temperature and normal pressure performed in the stirring step [C] can be performed in a short time, but it takes a long time to volatilize and remove the solvent after coating by the doctor blade method. Therefore, it is necessary to reduce the coating speed, and it becomes difficult to obtain productivity that is practical.

  Further, when the slurry viscosity exceeds 6.7 Pa · s and the solid content concentration exceeds 85% by mass, the fluidity of the slurry is deteriorated, and it takes time to defoam by subsequent stirring, and after standing still The slurry viscosity becomes too high, and the removal of air and dissolved oxygen in the slurry becomes insufficient. In addition, the coating process by the doctor blade method tends to cause streaks and variations in coating thickness. A green sheet with a uniform quality cannot be obtained. From this point of view, more preferable ultimate viscosity and solid content concentration at the time of the reduced pressure treatment are 55 to 80% by mass at 3.0 to 5.5 Pa · s at 20 ° C., more preferably 3.5 to 4.5 Pa · s. 60 to 75% by mass.

  In addition, as a container that may be used subsequently in the above-described reduced pressure stirring step [B] and the subsequent stirring step [C], a container with stirring blades is used in the milling step [A] of the previous step. In order to remove the solvent in the slurry dispersed in the slurry, the whole is uniformly stirred under reduced pressure without causing a region where stirring is partially insufficient. From this point of view, the container has a round bottom and a cylindrical shape, and the whole can be uniformly and uniformly stirred without causing a dead zone of stirring. Further, in order to efficiently remove the solvent, one provided with a jacket for heating the slurry outside the container can be preferably used.

  The preferable rotation speed of the stirring blade at this time is 10 to 60 rpm, and the stirring time is 1 to 50 hours, more preferably 20 to 40 rpm for 2 to 20 hours.

In the reduced pressure stirring step [B], the slurry in which the solvent is removed under reduced pressure and adjusted to the above suitable viscosity and solid content concentration is then stirred using a stirring blade immersed in the slurry at room temperature and normal pressure. Stir at 1.5 to 2.5 kW / m ³ , rotation speed: 5 to 20 rpm for 1 to 50 hours. In this stirring step [C], a large amount of air mixed or dissolved in the slurry as a result of the solvent in the slurry being boiled off in the above-mentioned reduced pressure stirring step [B] is floated and separated on the liquid surface. The agitation at this time employs the agitation power, rotation speed and agitation time in the above range in order to efficiently raise the bubbles in the slurry without involving outside air.

The stirring power of the stirring blade at this time is, for example, page 910 of “Chemical Engineering Handbook (5th revised edition)” (edited by the Chemical Engineering Association, published by Maruzen Co., Ltd., published on March 18, 1988). From the relationship between the power per unit area required for stirring the high-viscosity liquid described in 1 and the viscosity, the range of 1.5 to 2.5 kW / m ³ was adopted.

Incidentally, if the stirring power at this time is less than 1.5 kW / m ³ , the floating separation of the bubbles in the slurry can hardly be accelerated, and it takes a long time for the bubbles to dissipate. If it exceeds 5 kW / m ³ , air entrainment tends to occur due to the stirring, and on the contrary, bubble dissipation is delayed.

  Moreover, the reason why the stirring speed is set in the range of 5 to 20 rpm is that it is difficult to stably maintain ultra-low speed stirring of less than 5 rpm with a normal stirring motor, and reproducibility is difficult. It is because it will become easy to raise | generate the entrainment of air when it exceeds. A more preferable stirring speed under normal temperature and normal pressure is 5 to 10 rpm.

  In order to dissipate as much as possible the large amount of air mixed or dissolved in the pressure reduction stirring step [B] of the previous step by stirring with the stirring power and the number of revolutions, the stirring should be performed at room temperature and normal pressure for at least 1 hour. It is necessary to stir for 2 hours or more. Also, most of the bubbles that can be dissipated under the stirring conditions are dissipated within 10 hours or 20 hours. For example, even if stirring is continued for 50 hours or more, fine bubbles that cannot be removed are Since it is only rotating in the slurry accompanying the rotation, it is useless to continue stirring under these conditions.

  In addition, the kind of stirring blade used for stirring under the above normal temperature and normal pressure is not particularly limited, and is a disc turbine type, eight-paddle type, curved blade type, fan turbine type, arrow blade turbine type, fiddler type, bull margin type, inclined Paddle type, propeller type, or a combination of these blades in the top and bottom, as well as various types such as anchor type, helical screw type, helical ribbon type can be selected and used. The anchor type, helical screw type, and helical ribbon type agitators are particularly preferred for the degassing treatment of the highly viscous slurry that is the subject of the present invention.

  By stirring with a small stirring power as described above, most of the bubbles are released by floating and separating bubbles entrained in the slurry that has been degassed under reduced pressure. We thought that the air treatment was sufficient, and thereafter, the sheet was generated by the doctor blade method or the like. However, as a result of researches aimed at further densification and densification of the green sheet and eventually the zirconia-based sheet under the problems as described above by the present inventors, under the normal temperature and normal pressure as described above. Even with this gentle stirring, it was found that very fine bubbles simply accompanying the rotation of the stirrer did not cause deaeration, which hindered further increase in density.

  Therefore, in the present invention, in order to float as much as possible even the very fine bubbles that cannot be floated and separated by the gentle stirring, the standing step [D] for standing for a while after the stirring is added as an essential step. It was. The preferred time for standing still varies considerably depending on the slurry viscosity after the stirring treatment, so it is not possible to set a uniform standing time, but the floating separation of fine bubbles does not proceed sufficiently in a very short time, If it is too long, the solid component in the slurry will settle due to the difference in specific gravity and the uniformity will be lowered, so it is preferable to set it to 10 minutes or more and 25 hours or less depending on the slurry viscosity. In consideration of deaeration and workability, a more preferable standing time is 1 hour or more and 20 hours or less, more preferably 2 hours or more and 10 hours or less.

  More specifically, when the slurry viscosity is 2.7 Pa · s or more and less than 5.0 Pa · s, the slurry viscosity is 10 minutes or more and 5 hours or less, more preferably 20 minutes or more and 3 hours or less. When it is 0.0 Pa · s or more and 6.7 Pa · s or less, it is 30 minutes or more and 25 hours or less, more preferably 60 minutes or more and 10 hours or less. Although the standing time varies depending on the standing temperature conditions, it basically depends on the slurry viscosity. Therefore, if you want to shorten the standing time, warm the slurry components appropriately to the extent that they do not change. It is also effective to reduce the slurry viscosity.

  In this way, after leaving for a predetermined time, fine bubbles floating in the slurry also floated and dissipated on the liquid surface, and then formed into a sheet by a doctor blade method according to a conventional method and dried to almost completely complete the solvent component. The green sheet can be obtained by volatilization and removal. In forming the sheet, in order to improve the moldability and subsequent handling, it is preferable to apply a predetermined dry film thickness on a plastic film or the like, and dry with warm air at a temperature of about 40 to 120 ° C. . Preferably, for example, it is preferable to increase the running speed of the film by continuously drying with hot air in a drying furnace in which the temperature is sequentially increased, for example, 50 ° C., 80 ° C., and 100 ° C., because the productivity can be further increased.

  By adopting the coating slurry preparation method as described above, it is possible to obtain a green sheet that satisfies the above-mentioned requirements for the average pore diameter and the total pore volume.

  The zirconia green sheet thus obtained is preheated at 300 to 600 ° C. for 3 to 30 hours to decompose and disperse organic components such as a binder component, then preferably 1200 to 1500 ° C., more preferably 1300 to 1450 ° C. When baked for 1 to 5 hours, a smooth and homogeneous zirconia sheet with very few defects such as pinholes, voids, and craters can be obtained.

When this zirconia-based sheet is used for a solid electrolyte membrane of a fuel cell or a sensor, a preferable sheet thickness is 50 to 800 μm. This zirconia-based sheet uses the above-mentioned green sheet as a precursor, has a uniform thickness with very little variation in thickness, and the number of closed pores appearing in the sheet cross section is 90 × 65 μm ^2. When the number is 10 or less in this area, the Weibull coefficient of bending strength, which is an index of strength variation, is 10 or more, and the quality is extremely stable.

  The number of the closed pores corresponds to 90 μm × 65 μm of the sheet cross section when the longitudinal section of the sheet is observed with an ultra-deep color D shape measurement laser light microscope (manufactured by Keyence Corporation, trade name “VK-9500”). A 408 nm laser light micrograph (corresponding to about 1650 times) in which the portion was enlarged to 14.7 cm × 10.9 cm was taken, and the number of all pores that could be visually discriminated from the photograph was counted and determined.

  The ultra-deep color 3D shape measurement microscope used in the present invention irradiates the observation object from the objective lens with a 408 nm violet laser as a measurement laser light source, and accurately detects the focal position of the opposite light with a minimal pinhole. The high-precision linear scale is mounted on the condenser lens moving mechanism, and the resolution in the biaxial direction (height measurement) is 0.01 μm.

Therefore, the apparatus can perform an enlarged analysis comparable to that of an SEM, and can analyze the surface shape with high accuracy in a non-contact and non-destructive manner in a normal atmosphere. Moreover, since it can be measured in a non-destructive and normal atmosphere, it can be applied to the measurement of the green sheet without any trouble. The longitudinal section of the green sheet is observed in the same manner, and a portion corresponding to 90 × 65 μm ² in the cross section of the green sheet is 14 A 408 nm laser light microscope photograph (corresponding to about 1650 times) enlarged to 0.7 cm × 10.9 cm was taken, and the number of all pores that could be visually discriminated from the photograph was counted and determined. Therefore, as a matter of course, in the present invention, the number of closed pores in the longitudinal section of the green sheet is 10 or less in the same region.

  The bending strength of the sheet subject to the Weibull coefficient shall be the three-point bending strength specified in JIS R1601, the specimen shall be 50 mm x 8 mm in strip shape, 50 to 800 μm thick, and between the lower fulcrum The distance was 30 mm.

Next, the type of zirconia-based powder used as a raw material in the present invention is not particularly limited, but scandium oxide, yttrium oxide, ytterbium oxide are particularly suitable for use as a solid electrolyte membrane for fuel cells and sensors. Is a stabilized zirconia-based powder in which at least one oxide selected from 1 to 3 is added to zirconia as a stabilizer. This powder preferably has a specific surface area of 3 to ²⁰ m ² / g.

Also this _{powder, SiO 2, Al 2 O 3} , GeO 2, SnO 2, TiO 2, Sb 2 O 3, Ta 2 O 5, Nb 2 O 5, Bi 2 O 3 or the like is included as another oxide A mixture of the stabilized zirconia powder with about 0.1 to 5% by mass of alumina, titanium, and ceria is preferably used.

By the way, if the raw material powder has a relatively coarse particle surface with a specific surface area of less than 3 m ² / g, the sinterability when the green sheet is fired to form a zirconia-based sheet is lowered, and the relative density exceeds 95%. In particular, it is difficult to obtain a dense material exceeding 98%, and the sheet strength is insufficient. On the other hand, if the specific surface area is excessively finer than 20 m ² / g, the amount of binder used increases and the slurry viscosity increases, degassing at the slurry stage becomes difficult, and pore defects tend to remain. The denseness also tends to decrease, and warpage and undulation are likely to occur in the fired sheet. The more preferable specific surface area of the zirconia powder is 5 m ² / g or more and 16 m ² / g or less.

  There is no particular limitation on the type of binder used in the present invention, and conventionally known organic or inorganic binders can be appropriately selected and used. Examples of organic binders include ethylene copolymers, styrene copolymers, acrylate and methacrylate copolymers, vinyl acetate copolymers, maleic acid copolymers, vinyl butyral resins, and vinyl acetal resins. And vinyl formal resins, vinyl alcohol resins, waxes, celluloses such as ethyl cellulose, and the like.

  Among these, from the viewpoints of green sheet moldability, punching workability, strength, thermal decomposability during firing, and the like, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, etc. Alkyl acrylates having an alkyl group having 10 or less carbon atoms; and 20 carbon atoms such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, dodecyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, etc. Alkyl methacrylates having the following alkyl groups: hydroxyethyl acrylate, hydro Hydroxyalkyl acrylates or hydroxyalkyl methacrylates having a hydroxyalkyl group such as cyclopropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate; aminoalkyl acrylates or aminoalkyl methacrylates such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate; A number average molecular weight of 20,000 to 200,000 obtained by polymerizing or copolymerizing at least one of carboxyl group-containing monomers such as acrylic acid, maleic acid, maleic acid half ester such as monoisopropyl malate, More preferably, 50,000 to 100,000 (meth) acrylate copolymer is recommended. These organic binders can be used alone or in combination of two or more as necessary. Particularly preferred is a copolymer of monomers containing 60% by mass or more of isobutyl methacrylate and / or 2-ethylhexyl methacrylate.

  As the inorganic binder, zirconia sol, silica sol, alumina sol, titania sol and the like can be used alone or in admixture of two or more.

  The use ratio of the zirconia-based powder and the binder is not particularly limited, but is preferably in the range of 5 to 30 parts by mass, more preferably 10 to 20 parts by mass with respect to the former 100 parts by mass.

  Examples of the solvent include alcohols such as water, methanol, ethanol, 2-propanol, 1-butanol and 1-hexanol; ketones such as acetone and 2-butanone; aliphatic hydrocarbons such as pentane, hexane and heptane; Aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene; acetates such as methyl acetate, ethyl acetate and butyl acetate are appropriately selected and used. These solvents can also be used alone, or two or more of them can be appropriately mixed and used. The amount of these solvents to be used should be appropriately adjusted in consideration of the viscosity of the slurry.

  Plasticizers used as necessary are blended to impart flexibility to the green sheet. For example, phthalates such as dibutyl phthalate and dioctyl phthalate, glycols such as propylene glycol and glycols Ethers and the like are preferably used. The blending amount of these plasticizers is not particularly limited, but is preferably 0.5 to 5 parts by mass, more preferably 1 to 3 parts by mass with respect to 100 parts by mass of the zirconia powder.

  In the preparation of the slurry, in order to promote peptization and dispersion of the ceramic raw material powder, polymer electrolytes such as polyacrylic acid and ammonium polyacrylate, organic acids such as citric acid and tartaric acid, isobutylene or styrene and maleic anhydride And a dispersing agent comprising a copolymer of styrene and an ammonium salt thereof, a copolymer of butadiene and maleic anhydride and an ammonium salt thereof; and a surfactant or an antifoaming agent are added as necessary. be able to.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and is suitable as long as it can meet the purpose described above and below. Of course, it is possible to carry out with modifications, and these are all included in the technical scope of the present invention.

Example 1
3 parts by mass of yttria-stabilized zirconia-based powder (manufactured by Sumitomo Osaka Cement Co., Ltd .: trade name “OZC-3Y”, specific surface area: 8 m ² / g, average particle size: 0.6 μm) and alumina powder (Showa Denko) Company: Trade name “AL-160SG”) For 0.5 parts by mass of the mixture, methacrylic acid ester copolymer (2-ethylhexyl methacrylate; 95%, dimethylaminoethyl methacrylate; 4%, hydroxypropyl acrylate; 1 % Of copolymer, average molecular weight: 80,000, glass transition point: −9 ° C.) 14 parts by mass in terms of solid content, 2 parts by mass of dibutyl phthalate as plasticizer, toluene / isopropyl alcohol (as solvent) 50 parts by mass of a mixed solvent having a mass ratio of 3/2), an internal volume of 1 in which zirconia balls having a diameter of 10 mm are charged Placed in a nylon resin-made ball mill 0L, the raw material slurry was prepared by 40 hours milled at about 45 rpm. The slurry had a viscosity of 0.8 Pa · s at room temperature (25 ° C.).

This slurry was transferred to a jacketed round bottom cylindrical vacuum degassing vessel equipped with a vertical stirrer and having a volume of 50 L. While the stirrer was rotated at a speed of 30 rpm, the slurry was reduced in pressure at a jacket temperature of 40 ° C. 160 torr) under reduced pressure, and the viscosity was adjusted to 3.0 Pa · s. The solid content concentration of this slurry was approximately 60% by mass, calculated backward from the amount of the recovered solvent. Next, nitrogen gas was introduced into the container, and the stirrer (stirring power; 2 kW / m ³ ) was rotated at 10 rpm for 10 hours under normal temperature and normal pressure. After that, the stirrer was stopped and stopped to stand at room temperature (about 20 C.) for 2 hours to obtain a slurry for coating (solid content concentration: about 60% by mass).

  The obtained slurry for coating is transferred to a slurry dam of a coating apparatus, coated on a polyethylene terephthalate (PET) film by a doctor blade method, and a dryer (50 ° C., 80 ° C., 110 ° C. following the coating part). 3 zone) was passed at a speed of 0.2 m / min and dried to obtain a green sheet having a thickness of about 180 μm.

  This green sheet is cut into a width of 10 mm and a length of 350 mm, rounded into a spring, and inserted into a sample tube. This sample tube is attached to an automatic porosimeter “Autopore III9420” manufactured by Micromeritex, : The average pore diameter and the total pore volume in the green sheet were determined at 1 to 60000 psia.

  Further, the obtained green sheet is cut into a strip of about 60 mm × 10 mm, and the upper and lower sides are degreased by sandwiching the surface with a flat 99.5% alumina porous plate, followed by firing at 1350 ° C. for 3 hours. Thus, a 3 mol% yttria-stabilized zirconia-based sheet having a thickness of 50 mm × 8 mm and a thickness of 150 μm was obtained.

  The cross-sections at 10 different positions of the obtained zirconia-based sheet and green sheet were photographed with a 408 nm laser light microscope, and the number of closed pores was examined visually from a laser light micrograph magnified 1650 times. Further, a three-point bending strength test was performed at room temperature in accordance with JIS R1601, and the Weibull coefficient was calculated.

  The results are shown in Table 1.

Example 2
10 mol% scandia-1 mol% ceria-stabilized zirconia powder (made by Daiichi Rare Elemental Chemical Co., Ltd .: trade name “10Sc1CeSZ”, specific surface area: 9 m ² / g, average particle size: 0.5 μm) A slurry was prepared in the same manner as in Example 1 except that the above was used.

  The slurry was transferred to a jacketed round bottom cylindrical vacuum degassing vessel having a volume of 50 L equipped with a vertical stirrer, and the pressure was reduced at a jacket temperature of about 45 ° C. while rotating the stirrer at a speed of 30 rpm (30 ° C. The viscosity was adjusted to 4.0 Pa · s. The solid content concentration of this slurry was about 70% by mass calculated backward from the amount of the recovered solvent. Next, nitrogen gas was introduced into the container, and the stirring was performed by rotating the stirrer at 15 rpm for 5 hours at normal temperature and pressure. Then, the stirrer was stopped and held for 1 hour in a stationary state to obtain a slurry for coating (solid content concentration: about 70% by mass).

  Using the obtained coating slurry, a green sheet having a thickness of about 680 μm was obtained in the same manner as in Example 1, and the average pore diameter and the total pore volume of the green sheet were examined in the same manner.

  Further, in the same manner as in Example 1, the green sheet was fired at 1400 ° C. for 3 hours to obtain a 10 mol% scandia-1 mol% ceria stabilized zirconia-based sheet having a thickness of about 500 μm. In addition, the number of closed pores was examined with a laser light microscope in which the cross section of the green sheet was magnified 1650 times, and the three-point bending strength and Weibull coefficient at room temperature were determined. The results are shown in Table 1.

Reference example 1
Zirconia powder (made by Daiichi Rare Elemental Chemical Co., Ltd .: trade name “EPR”, specific surface area: 18 m ² / g, average particle size: 0.3 μm) and commercially available ytterbium oxide powder to 5 mol% with respect to zirconia A slurry was prepared in the same manner as in Example 1 except that it was used as a zirconia-based raw material powder.

  This slurry was transferred to a jacketed round bottom cylindrical vacuum degassing vessel equipped with a bowl-shaped stirrer and having a volume of 50 L, and the pressure was reduced at room temperature (about 20 ° C.) while rotating the stirrer at a speed of 30 rpm. The viscosity was adjusted to 6.0 Pa · s by concentration and defoaming under 30 to 160 psia). The solid content concentration of this slurry was about 75% by mass calculated backward from the amount of the recovered solvent. Next, nitrogen gas was introduced into the container, and the stirring was performed by rotating the stirrer at 7 rpm for 20 hours at room temperature and normal pressure. Then, the stirrer was stopped and held for 4 hours in a stationary state to obtain a slurry for coating (solid content concentration: about 75% by mass).

  Using the obtained coating slurry, a green sheet having a thickness of about 250 μm was obtained in the same manner as in Example 1, and the average pore diameter and the total pore volume of the green sheet were examined in the same manner.

  Further, in the same manner as in Example 1, the green sheet was fired at 1400 ° C. for 3 hours to obtain a 5 mol% ytterbia-stabilized zirconia-based sheet having a thickness of about 200 μm. The number of closed pores was examined by a 408 nm laser light microscope photograph magnified 1650 times, and the three-point bending strength and Weibull coefficient at room temperature were determined. The results are shown in Table 1.

Comparative Example 1
A slurry was prepared in the same manner as in Example 1 above, and this slurry was transferred to a round bottom cylindrical vacuum degassing vessel with a 50 L internal volume equipped with a vertical stirrer, and the stirrer was rotated at a speed of 30 rpm. The mixture was concentrated and degassed under reduced pressure (30 to 160 psia) at a jacket temperature of about 20 ° C. while adjusting the viscosity to 3.0 Pa · s. The solid content concentration of this slurry was approximately 60% by mass, calculated backward from the amount of the recovered solvent. Next, nitrogen gas was introduced into the container, and the stirrer was rotated at 10 rpm for 20 hours at room temperature and normal pressure, followed by stirring to obtain a slurry for coating (solid content concentration: about 60% by mass).

  The obtained slurry for coating was immediately sent to the coating machine without maintaining a stationary state, and a green sheet having a thickness of about 180 μm was obtained in the same manner as in Example 1 above. The pore size and total pore volume were investigated.

  Further, in the same manner as in Example 1, the green sheet was fired at 1350 ° C. for 3 hours to obtain a 3 mol% yttria-stabilized zirconia-based sheet having a thickness of about 150 μm. The number of closed pores was examined by a 408 nm laser light microscope photograph magnified 1650 times, and the three-point bending strength and Weibull coefficient at room temperature were determined. The results are shown in Table 1.

Comparative Example 2
A slurry was prepared in the same manner as in Example 1, and this slurry was transferred to a jacketed round bottom cylindrical vacuum degassing vessel equipped with a vertical stirrer and having a volume of 50 L. The stirrer was moved at a speed of 30 rpm. While rotating, it was concentrated and degassed under reduced pressure (30 to 160 psia) at a jacket temperature of 50 ° C. to adjust the viscosity to 3.0 Pa · s. The solid content concentration of this slurry was approximately 60% by mass, calculated backward from the amount of the recovered solvent. Next, nitrogen gas was introduced into the container, and the mixture was allowed to stand at room temperature and normal pressure for 1 hour without stirring to obtain a slurry for coating (solid content concentration: about 60% by mass).

  Using this coating slurry, a green sheet having a thickness of about 180 μm was obtained in the same manner as in Example 1, and the average pore diameter and total pore volume of the green sheet were examined in the same manner.

  Further, in the same manner as in Example 1, the green sheet was fired at 1350 ° C. for 3 hours to obtain a 3 mol% yttria-stabilized zirconia-based sheet having a thickness of about 150 μm. The number of closed pores was examined using a laser light micrograph magnified 1650 times, and the three-point bending strength and Weibull coefficient at room temperature were determined. The results are shown in Table 1.

Comparative Example 3
A slurry was prepared in the same manner as in Example 1 above, and this slurry was transferred to a round bottom cylindrical vacuum degassing vessel with a 50 L internal volume equipped with a vertical stirrer, and the stirrer was rotated at a speed of 30 rpm. The mixture was concentrated and degassed under reduced pressure (30 to 160 psia) at a jacket temperature of 60 ° C. while adjusting the viscosity to 7.5 Pa · s. The solid content concentration of this slurry was approximately 60% by mass, calculated backward from the amount of the recovered solvent. Next, nitrogen gas is introduced into the container, and the stirrer is rotated at 35 rpm at room temperature and normal pressure for 10 hours to stir. Thereafter, stirring is stopped and the slurry is left to stand for 40 hours (solid content concentration: About 60% by mass).

  The obtained coating slurry is sent to a coating machine to obtain a green sheet having a thickness of about 180 μm in the same manner as in Example 1, and the average pore diameter and the total pore volume of the green sheet are similarly examined. It was.

  Further, in the same manner as in Example 1, the green sheet was fired at 1350 ° C. for 3 hours to obtain a 3 mol% yttria-stabilized zirconia-based sheet having a thickness of about 150 μm. The number of closed pores was examined by a 408 nm laser light microscope photograph magnified 1650 times, and the relative density at room temperature, the three-point bending strength, and the Weibull coefficient were determined by the Archimedes method. When photographing, the surface of the longitudinal section was not subjected to surface treatment, and the images were taken as they were at five arbitrary locations, the number of closed pores was measured for each, and the average value was taken as the number of closed pores. The results are shown in Table 1.

  A laser light micrograph of the sheet longitudinal section obtained in Example 1 is shown in FIG. 1, and a laser light micrograph of the sheet longitudinal section obtained in Comparative Example 2 is shown in FIG. The closed pores appearing in the photograph are black circular or elliptical, and the diameter is about 0.3 to 3 μm.

  From Table 1, it can be considered as follows.

Examples 1 and 2 in Table 1 are examples that satisfy the requirements of the present invention, and both the average pore diameter and total pore volume of the pores contained in the green sheet satisfy the requirements of the present invention. It can be seen that the number of closed pores is small and extremely dense. Therefore, the zirconia sheet obtained by firing this also has a high relative density and good bending strength, a relatively high Weibull coefficient, and a very small number of closed pores.

  On the other hand, in Comparative Example 1 in which the standing step [D] was omitted in the preparation stage of the coating slurry and in Comparative Example 2 in which the stirring step [C] was omitted, both the average pore diameter and the total pore volume of the green sheet Not only exceeds the specified range of the present invention, but also has a large number of closed pores, and the zirconia-based sheet obtained by firing this also has a relatively low relative density, a poor bending strength and a Weibull coefficient, and a closed pore number. Very many.

  Further, in Comparative Example 3 where the rotational speed of the stirring step [C] is too high, both the average pore diameter and the total pore volume of the green sheet are relatively large and the number of closed pores is large, and the zirconia system obtained by firing this The sheet also has a relatively low relative density, poor bending strength and Weibull coefficient, and a large number of closed pores.

2 is a laser light micrograph of a longitudinal section of a sheet obtained in Example 1. 4 is a laser light micrograph of a longitudinal section of a sheet obtained in Comparative Example 2.

Claims (7)

  A zirconia green sheet containing a zirconia powder and a binder and molded by a doctor blade method, wherein the average pore diameter of the pores present in the green sheet measured by a mercury intrusion method is 0.01-0. A zirconia-based green sheet having a total pore volume of 0.01 to 0.05 mL / g and having a size of 06 μm. ^2. The zirconia green sheet according to claim 1, wherein the number of closed pores observed by photographing a longitudinal section with a 408 nm laser light microscope is 10 or less in a region of 90 × 65 μm ² . The zirconia-based powder contains 3 to 12 mol% as a stabilizer of at least one oxide selected from the group consisting of scandium oxide, yttrium oxide and ytterbium oxide, and has a specific surface area of 3 to ²⁰ m ² / The zirconia green sheet according to claim 1 or 2, which is g. Zirconia-based green sheet according to any one of the claims 1-3, der those fired at 1300 to 1500 ° C.,
A zirconia sheet having a thickness of 50 to 800 μm and having 10 or less closed pores in a 90 × 65 μm ² region observed by taking a photograph of a longitudinal section of the sheet with a 408 nm laser light microscope . The zirconia sheet according to claim 4 , wherein the Weibull coefficient of bending strength is 10 or more. The zirconia-based sheet according to claim 4 or 5 , which is used as a solid electrolyte membrane for a fuel cell or a sensor. A method for producing the zirconia green sheet according to any one of claims 1 to 3,
[A] A milling step of milling a raw material containing a zirconia-based powder, a binder and a solvent to obtain a slurry having a viscosity of 1.5 Pa · s or less,
[B] The slurry was removed under reduced pressure so that the viscosity at 20 ° C. was in the range of 2.7 to 6.7 Pa · s in a vessel equipped with stirring blades, and the solid content concentration was 50 to 85% by mass. A vacuum stirring step to obtain a slurry,
[C] Stirring the resulting slurry with stirring blades immersed in the slurry at room temperature and normal pressure, stirring power: 1.5 to 2.5 kW / m ³ , rotation speed: 5 to 20 rpm, and stirring for 1 to 50 hours Process,
[D] Then, the stationary process of leaving still for 10 minutes-25 hours, without rotating a stirring blade,
A method for producing a zirconia green sheet, wherein the slurry obtained by the above method is used and the sheet is formed by a doctor blade method.