JPH07272733A - Manufacture of porous sintered body - Google Patents

Abstract

PURPOSE:To control distributing porosity of a porous sintered body to an object value by one time burning process, in the case of manufacturing the porous sintered body by burning a long scaled ceramics molded body. CONSTITUTION:A ceramics molded body 1, in a condition held in a perpendicular direction, is burned to manufacture a porous sintered body. By controlling the temperature in a lengthwise direction of the ceramics molded body l, porosity in a lengthwise direction of the porous sintered body is controlled. Preferably, an upper end part 1a of the ceramics molded body 1 is held, thus to suspend it in the perpendicular direction. Preferably, by setting a temperature in an upper side relatively higher than a temperature in a lower side of the ceramics molded body 1 at burning time, the difference of porosity in the lengthwise direction of the porous sintered body is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous ceramics sintered body, which is useful, for example, as a supporting member for a ceramics filter, a ceramics heater, a ceramics kiln tool, and a solid oxide fuel cell. The present invention relates to a method for manufacturing a porous sintered body.

[0002]

2. Description of the Related Art A slender porous sintered body such as a ceramic filter, a ceramic heater, a ceramic kiln tool, and a support member for a solid oxide fuel cell requires a process for firing a long ceramic molded body. In particular, straightness is required for each of these members, but when a long compact is installed laterally or horizontally and fired, the effect of gravity causes the long porous sintered compact to bend. Resulting in. Therefore, in order to maintain the straightness of the porous sintered body, it is general that the upper end portion of the ceramic molded body is fixed and hung down, and the ceramic molded body is fired in a state where gravity is applied in the vertical direction.

However, according to this method, the load of the molded body is applied near the upper end of the ceramic molded body, and such load is hardly applied near the lower end. As a result, it was found that there is a difference in the degree of firing shrinkage between the upper end portion and the lower end portion of the molded body during the firing shrinkage stage. That is, since the load of the compact is applied at the upper end of the compact, the degree of shrinkage due to firing is relatively small, and the degree of shrinkage at the lower end of the compact is relatively high. It was found that there is a large difference in porosity between the parts.

In order to solve such a problem, the applicant of the present invention discloses in Japanese Patent Application Publication No. 6-10114 that a long molded body is first hung and primary fired, and then the molded body is turned upside down. A method for suppressing the difference in porosity between the upper and lower sides of a long porous sintered body by (inverting the molded body) and then performing secondary firing has been disclosed. According to this method, especially by controlling the conditions such as the temperature of the primary firing and the secondary firing, the difference between the upper and lower porosities and the like can be suppressed considerably.

[0005]

However, when the present inventor tried the method of Japanese Patent Application Publication No. 6-10114, it became clear that the following problems would occur. That is,
Recently, the length of the porous sintered body tends to increase. In particular, a lanthanum manganite sintered body is currently regarded as promising as an air electrode material for a solid oxide fuel cell (Energy Engineering, 13, 2, 52-68, 19).
90 years). As such lanthanum manganite sintered bodies, those having a substantially stoichiometric composition and those having a partial loss of A site (lanthanum site) (manganese-rich composition) are known. In particular, a supporting member made of a porous sintered body made of lanthanum manganite in which A site is doped with Ca or Sr is regarded as promising as a self-supporting electrode material which also serves as an air electrode. Further, a support member made of zirconia is widely used as a support member for a solid oxide fuel cell.

In such a use as a support member for a solid oxide fuel cell, it is required to increase the length of the support member from the viewpoint of power generation efficiency, and recently, 2 m.
Those of the above length are produced. However, the step of suspending such a large-length ceramic molded body for primary firing, after primary firing, removing this porous sintered body from the firing furnace, turning it upside down, and hanging it again from a predetermined device is It is extremely troublesome, difficult, and labor intensive. After the primary firing is finished, first lower the temperature of the firing furnace to room temperature, then after removing the above-mentioned porous sintered body, reversing, and re-installing the work, reheat the firing furnace again. Need to rise. Therefore, from the viewpoint of thermal efficiency and productivity, it is very wasteful and causes a cost increase.

An object of the present invention is to enable the distribution of the porosity of the porous sintered body to be controlled to a desired value in one firing step when firing a long ceramic molded body. Is.

[0008]

According to the method for producing a porous sintered body of the present invention, when a long ceramic molded body is fired while being held in the vertical direction, It is characterized in that the porosity in the length direction of the porous sintered body is controlled by controlling the temperature.

[0009]

The present inventor has examined the reason why there is a difference in porosity between the upper end and the lower end of the porous sintered body. At this time, the load of the molded body is applied to the upper end portion when the molded body is suspended, but the dimensional change of the molded body due to this load did not occur in the stage before firing. Therefore, at the stage where this molded product undergoes firing shrinkage, the amount of firing shrinkage is small in the portion where a large load is applied, and the amount of firing shrinkage is relatively large in the portion where only a small load is applied.

Based on this knowledge, the inventor of the present invention can control the degree of firing shrinkage of each part in the longitudinal direction (vertical direction) of the molded body by controlling the temperature in the longitudinal direction of the ceramic molded body. It is possible, and it is possible to control the porosity in the length direction of the porous sintered body by this,
The present invention has been reached.

Specifically, when suspending a ceramic molded body in a firing furnace, a plurality of heaters are installed in the vertical direction of the firing furnace, and the calorific value of each heater is controlled independently of each other. The temperature of each part of the body length can be controlled.

In carrying out the method of the present invention, preferably, the upper end of the ceramic molded body is held so that the ceramic molded body is suspended vertically. However, it is not always necessary to hold the upper end of the molded body,
For example, it is possible to hold the molded body in the vertical direction by holding the central portion of the molded body or by holding the lower end portion of the molded body.

As described above, the porosity in the length direction of the long porous sintered body can be controlled by one firing, and as a result, the ceramic molded body can be inverted and secondarily fired as in the conventional case. It is not necessary to do so, and a porous sintered body having a desired porosity distribution can be obtained in a single firing step. Therefore, the troublesome work of inverting the compact is unnecessary, and the waste of lowering the temperature of the firing furnace to room temperature and raising the temperature again can be prevented. Therefore, the manufacturing cost can be greatly reduced.

[0014]

EXAMPLES In particular, when manufacturing the above-mentioned ceramic filter as a porous sintered body or a supporting member for a solid oxide fuel cell, pores, especially pores, are formed over the entire length of the porous sintered body. The rates need to be uniform. That is,
In the case of a ceramics filter, if the porosity and the microstructure of each part in the length direction are different, the characteristics as a filter deteriorate.

Further, in the case of the above-mentioned supporting member made of zirconia and the self-supporting air electrode supporting member of the solid oxide fuel cell, the air electrode membrane, the solid electrolyte membrane and the air contact through this supporting member. Since air is supplied to the three-phase interface, it is necessary to make the pressure loss of the support member uniform and the state of the three-phase interface uniform to make the power generation performance uniform in the length direction. Therefore, in the application of the support member of the solid oxide fuel cell, the demand for uniform porosity is particularly severe.

As described above, when it is desired to control the porosity of the long porous sintered body to be uniform in the length direction, the temperature in the length direction is controlled as follows. . That is, when firing is performed at the same temperature in the length direction of the molded body, as described above, a relatively large load is applied to the relatively upper portion of the ceramic molded body, so that the firing shrinkage amount is small. And the porosity increases. On the other hand, since a relatively small load is applied to the lower portion, the amount of shrinkage by firing becomes relatively large and the porosity becomes small.

Therefore, when the temperature of the upper side of the molded body is made relatively higher than the temperature of the lower side during firing, the firing is accelerated in the upper side. As a result, the amount of firing shrinkage on the upper side becomes larger, so the difference in the amount of firing shrinkage on the upper side and the lower side is
Compared to the case where the overall firing temperature is constant, it becomes smaller.

In this case, the temperature difference in the vertical direction of the ceramic molded body during firing is 30 ° C or more,
It is preferably 50 ° C or lower. By setting this difference to 30 ° C. or more, the above-mentioned difference in porosity is further reduced. When the difference exceeds 50 ° C, the effect of the progress of sintering due to the temperature difference is greater than the effect of the load, and the porosity of the upper end is lower than that of the lower end. Tends to be smaller.

When the supporting member of the solid oxide fuel cell is an air electrode, the material can be applied to manganite generally having a perovskite structure, but lanthanum manganite is particularly preferable. In this lanthanum manganite, calcium, strontium, aluminum, cobalt, magnesium, nickel, chromium, copper,
It may contain one or more substituted metal atoms selected from the group consisting of iron, titanium and zinc.

When manufacturing the inside of the ceramic molded body,
Preferably, the raw material powder is mixed with at least a pore-forming agent and a binder to be molded. The pore-forming agent disappears at a relatively low temperature, and acrylic powder, carbon powder, cellulose and the like are preferable. As the binder, polyvinyl alcohol, methyl cellulose, acrylic binder and the like are preferable.

In the case of a support member for a solid oxide fuel cell, the firing temperature of the molded body is 1300 ° C to 1600 ° C.
It is preferable that If the firing temperature is less than 1300 ° C, sintering will not be completed completely. When it is higher than 1600 ° C, the structure of the sintered body becomes too dense.

The air electrode substrate used as a self-supporting supporting member of a solid oxide fuel cell is used as a base material of a unit cell, and a solid electrolyte membrane, a fuel electrode film, Each component such as an interconnector and a separator is laminated. At this time, the shape of the air electrode substrate may be a cylindrical shape with both ends open, a bottomed cylindrical shape with one end open and the other end closed, or a flat plate shape. Of these, any of the above-mentioned cylindrical shapes is particularly preferable because thermal stress is less likely to be applied and gas sealing is easy.

The porosity of the porous sintered body is preferably 5-40%. When it is used as a support member for a solid oxide fuel cell, the porosity is further increased to 15 to
It is preferably 40%, and more preferably 25-35%. In this case, by setting the porosity of the air electrode to 15% or more, the gas diffusion resistance is reduced and the porosity is set to 40%.
By setting the content to be less than or equal to%, it is possible to secure some strength.

Hereinafter, more specific experimental results will be described. (Relationship between Set Temperature of Heater in Firing Furnace and Measured Temperature) First, the inside of the firing furnace is divided into 9 regions or zones, and heaters are installed corresponding to the respective regions, and the temperature of each heater is set to 1540. The temperature was set to a predetermined temperature within the range of ° C to 1600 ° C. On the other hand, a thermocouple was installed in each area, each heater was caused to generate heat, and the difference between the set temperature of the heater in each area and the measured temperature of the thermocouple in each area was calculated. As a result, the difference between the set temperature of the heater in each area and the measured temperature of the thermocouple in each area is 0 ° C to 2 ° C.
Met. Therefore, the set temperature of the heater in each area could be considered to be almost the same as the actual measured temperature in each corresponding area.

(Production of Ceramic Molding) Raw material powders of La ₂ O ₃ , CaCO ₃ and Mn ₃ O ₄ were used as starting raw materials. A predetermined amount of starting raw material powder was weighed and mixed so that the composition ratio was La _0.80 Ca _0.20 MnO ₃ . This mixed powder was molded by a cold isostatic press method at a pressure of 1 tf / cm ² to prepare a molded body. This molded body was heat-treated in the air at 1580 ° C. for 10 hours to synthesize a perovskite complex oxide having a composition ratio of La _0.80 Ca _0.20 MnO ₃ .

This composite was prepared by wet trommel.
Grinded using zirconia boulders, average particle size 5.8μm
The synthetic powder of was produced. Next, to this synthetic powder, water,
Add an acrylic binder as an organic binder,
The mixture was mixed to prepare a slurry having a water content of 40% and granulated with a spray dryer. Then, this granulated powder and acrylic powder as a pore-forming agent were dry-mixed and extrusion-molded to obtain a tubular molded body having a length of 2300 mm and an outer diameter of 25 mm.

(Holding Method for Molded Product 1) The molded product 1 was suspended as schematically shown in FIG. Specifically, a through hole is provided in the upper end portion 1a of the molded body 1, the support rod 3 is inserted into the through hole, both ends of the support rod 3 are bridged over the support base 2, and the molded body 1 is suspended. . Then, the respective temperatures at the measurement positions a, b, c, d and e shown in FIG. 1 were controlled.

However, the measurement position a is 100 mm from the upper end surface of the molded body 1, and the measurement position b is the molded body 1
500 mm from the upper end surface of the
It is 1000 mm from the upper end surface of the molded body 1, the measurement position d is 1500 mm from the upper end surface of the molded body 1, and the measurement position e is 2200 m from the upper end surface of the molded body 1.
It is in the m position.

(Comparative Example) In particular, the molded body was fired without controlling the temperature in each region. That is, each measurement position a,
Each firing temperature in b, c, d and e was set to 1,595 ° C.
Set to.

(Examples 1 to 3) The temperature was controlled in each region, and the molded body was fired. That is, each measurement position a, b,
The firing temperatures for c, d and e were set as shown in Table 1, and firing was performed in this state. The firing time was hours.

With respect to the long porous sintered body produced by each of these examples, the respective measurement positions a, b, c,
For d and e, the porosity was measured by the water displacement method. The results are shown in Table 1.

[0032]

[Table 1]

As can be seen from Table 1, in the comparative example, the porosity gradually decreases from the measurement position a to e. This is considered to be because, as described above, the degree of firing shrinkage is affected by the load applied to each measurement position of the molded body during the firing shrinkage stage. This difference reached 3.8% between the measurement positions a and e.

FIG. 2 is a scanning electron micrograph showing the ceramic structure at the measurement position a in Comparative Example 1, and FIG. 3 is a scanning electron micrograph showing the ceramic structure at the measurement position e in Comparative Example 1. Is. Measurement position a
It can be seen that the sintering progresses at the measurement position e rather than at.

In Example 1, the difference in porosity between the measurement positions a and e is reduced to 0.9%. This is probably because the firing temperature was gradually decreased from the measurement position b to e, and as a result, the progress of firing shrinkage was suppressed. In addition, the temperature difference between the upper end and the lower end is 30
By setting the temperature to ° C or higher, the difference in porosity can be significantly suppressed to 1% or less.

In Example 2, the difference in porosity between the measurement positions a and e was reduced to 0.5%. In particular, considering other experimental results as well, by maintaining the temperature difference between the upper end portion and the lower end portion within the range of 35 ° C to 45 ° C, the difference in porosity between the upper end portion and the lower end portion is It was found that it can be significantly suppressed to 0.5% or less.

FIG. 4 is a scanning electron micrograph showing the ceramic structure at the measurement position a in Example 2, and FIG. 5 is a scanning electron micrograph showing the ceramic structure at the measurement position e in Example 2. Is. Measurement position a
It is understood that the degree of progress of sintering is almost the same at the measurement position e as well.

In Example 3 as well, the difference in porosity between the measurement positions a and e was reduced to 2.0%, which is a significant improvement over the comparative example. However, as a result of the temperature difference between the upper end portion and the lower end portion exceeding 50 ° C, the upper end portion is more shrunk by firing than the lower end portion, and the upper end portion has a smaller porosity. I found out.
Therefore, if this temperature difference exceeds 50 ° C and becomes large,
Since the difference in porosity between the upper end portion and the lower end portion becomes larger, it can be said that it is more preferable to keep the temperature difference at 50 ° C. or less from this viewpoint.

Further, the present inventor now sets the temperature at the measuring position a to 1540 ° C. and the temperature at the measuring position b to 1550 ° C.
C, the temperature at the measurement position c is 1560 ° C, the temperature at the measurement position d is 1570 ° C, and the temperature at the measurement position e is 1
The temperature was set to 580 ° C. As a result, the porosity of the upper end was set to about 35%, and the porosity of the lower end was set to about 25%. Such a large porosity difference is extremely difficult to realize in the conventional firing method, especially when a gas furnace is used.

The present inventor has further found that La _0.80 Sr _0.20 Mn
A firing test similar to the above was carried out on a tubular shaped body having a length of 2300 mm and an outer diameter of 25 mm and made of a complex oxide having a perovskite structure having a composition of O ₃ , and the same result as the above was obtained.

[0041]

As described above, according to the present invention, when firing a long ceramic molded body, the porosity distribution of the porous sintered body can be controlled by one firing step. You can control the value.

[Brief description of drawings]

FIG. 1 is a front view schematically showing a state in which a ceramic molded body 1 is suspended and fired.

2 is a scanning electron micrograph showing a ceramic structure at a measurement position a in Comparative Example 1. FIG.

3 is a scanning electron micrograph showing a ceramic structure at a measurement position e in Comparative Example 1. FIG.

FIG. 4 is a scanning electron micrograph showing a ceramic structure at a measurement position a in Example 2.

5 is a scanning electron micrograph showing a ceramic structure at a measurement position e in Example 2. FIG.

[Explanation of symbols]

1 Long ceramic molded body 1a Upper end 2
Supports a, b, c, d, e Temperature setting position and porosity measuring position

Claims (5)

[Claims] 1. A method for producing a porous sintered body by firing a long ceramic compact while holding it in the vertical direction, by controlling the temperature of the ceramic compact in the longitudinal direction. A method for producing a porous sintered body, comprising controlling the porosity in the lengthwise direction of the porous sintered body. 2. The method for producing a porous sintered body according to claim 1, wherein an upper end portion of the ceramic formed body is held and thereby the ceramic formed body is suspended in the vertical direction. 3. The difference in porosity in the length direction of the porous sintered body is reduced by making the temperature of the upper side of the ceramic molded body during the firing relatively higher than the temperature of the lower side. The method for producing a porous sintered body according to claim 1 or 2, characterized in that. 4. The production of a porous sintered body according to claim 3, wherein the temperature difference in the vertical direction of the ceramic molded body during the firing is 30 ° C. or more and 50 ° C. or less. Method. 5. The method for producing a porous sintered body according to claim 3, wherein the porous sintered body is a support member for a solid oxide fuel cell.