JP2001130978A - Method for producing porous sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a porous sintered compact having a fixed pore diameter without changing the kind of a blowing agent to be added to a slurry, the concentration of the blowing agent, viscoelasticity of the slurry, particle diameter and particle shape of raw material powder contained in the slurry, a time that the foamy slurry loses fluidity by crosslinking polymerization. SOLUTION: In this method for producing the porous sintered compact comprising a process for preparing the slurry of raw material powder and an organic substance to be cured by crosslinking polymerization, a process for foaming the slurry to give a foamy slurry, a process for adding a crosslinking agent to the foamy slurry and feeding the slurry into a mold, a process for curing the foamy slurry by crosslinking polymerization to give a molding product and a process for sintering the molding product, in the process for introducing the slurry to the mold, foams are expanded or compressed by decompression or compression and the molding product is cured while maintaining the state control the pope diameter of the porous sintered compact.

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 sintered body having a controlled pore diameter and used for a filter, a heat insulating material, a catalyst carrier, a heater, a sound absorbing material and the like.

[0002]

2. Description of the Related Art Conventionally, a porous sintered body has been manufactured by the following method. That is, a slurry containing a raw material powder and a binder, a dispersant, a solvent, and the like is adjusted, a foaming agent is added to the slurry, and foaming is performed to a predetermined volume by stirring and / or gas introduction to form a foamy slurry. This is a method of producing a porous sintered body by casting into a mold and drying to obtain a molded body, and further sufficiently drying and then sintering.

[0003] In this method, in order to dry the foamy slurry into a molded article, it is necessary to dry the foamed slurry from the surface portion thereof. Are fixed at different times, so that the pores become large inside the molded body due to the coalescence of bubbles, and it is difficult to produce a porous sintered body having a uniform pore diameter. Furthermore, in the step of drying the foamy slurry in the mold, the molded body shrinks with the removal of the solvent, but at the initial stage, the surface on which the drying occurs is fixed first, and the tensile force is applied to the part to be finally dried. , The pore diameter inside becomes large, and a cavity (nest) may be formed.

[0004] In order to solve the above problems, an organic substance which can be cured by cross-linking polymerization is blended into a slurry to form a foamy slurry, a cross-linking agent is mixed, and the mixture is cast into a mold and cured to form a molded body. There is a method of obtaining (Patent No. 250650)
No. 2). According to this method, the pore size distribution in the molded article becomes uniform, and no voids (nests) are formed inside the molded article. Consequently, the pore diameters are uniform, and the voids (nests) are formed inside.
It is possible to obtain a much better porous sintered body without the conventional technology.

[0005] However, the above-mentioned method for producing a porous sintered body has the following problems to be further improved. In other words, the pore size is controlled by the type of foaming agent added to the slurry, the concentration of the foaming agent, the viscoelasticity of the slurry, the amount of gas introduced, the particle size and particle shape of the raw material powder contained in the slurry, and the crosslinking polymerization. Therefore, conditions that affect the foaming diameter in the foamed slurry, such as the time until the foamy slurry loses fluidity, are taken into consideration. For example, among the conditions described above, the conditions except the type of the foaming agent and the concentration of the foaming agent are fixed, and the type of the foaming agent and the concentration of the foaming agent are changed to change the surface tension and the liquid film strength of the bubbles. Taking advantage of this, there is a method of controlling the pore diameter in the sintered body by changing the bubble diameter that can exist stably.

However, in this method, it is necessary to consider the dispersion state of the raw material powder in the slurry and the reactivity with the organic substance which can be cured by cross-linking polymerization. There is little difference in the surfactant activity of the foaming agent having a good foaming property, and there is no significant difference in the bubble diameter that can be stably present in the foamy slurry. There is a problem that the width in which the pore diameter can be controlled is small.

Further, for example, conditions other than the time until the foamy slurry loses fluidity by cross-linking polymerization are fixed,
There is a method of controlling the pore diameter in the sintered body by changing the bubble diameter by utilizing the fact that the bubbles are united to increase the bubble diameter until the foamy slurry loses the fluidity. However, in this method, the type and concentration of the organic substance capable of cross-linking polymerization, the type and concentration of the cross-linking agent, the type and concentration of the cross-linking initiator, the conditions such as the temperature until the foamy slurry loses fluidity due to cross-linking polymerization. When the time is longer, the diameter of the bubbles present in the foamy slurry increases with the coalescence of the bubbles, but during this time the slurry moves downward due to its high density. For this reason, there is a problem that a density gradient or a pore diameter gradient occurs depending on a position at the time of pouring the porous sintered body, and uniformity is lost.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and includes a kind of a foaming agent added to a slurry, a concentration of a foaming agent, a viscoelasticity of the slurry, and a slurry. A method for producing a porous sintered body having a desired pore diameter without changing the particle size and shape of the raw material powder contained therein, and the time until the foamy slurry loses fluidity due to cross-linking polymerization. Is provided.

[0009]

The present invention provides the following method for solving the above-mentioned problems. 1) a step of preparing a slurry in which a raw material powder and an organic substance which is cured by cross-linking polymerization are dispersed or dissolved in a solvent, and adding a foaming agent to the slurry and foaming the foam by stirring and / or introducing gas; A step of adding a crosslinking agent and / or a crosslinking initiator to the foamy slurry and introducing the mixture into a mold; a step of curing the foamy slurry by crosslinking polymerization to form a molded body; In the method for producing a porous sintered body, which comprises a step of drying and sintering the body, in the step of introducing into the mold, bubbles are expanded by decompression, and a foamy slurry is cross-linked while maintaining the depressurized state. A method for producing a porous sintered body, comprising controlling the pore diameter of the porous sintered body by curing by polymerization. 2) a step of preparing a slurry in which a raw material powder and an organic substance which is cured by cross-linking polymerization are dispersed or dissolved in a solvent, and adding a foaming agent to the slurry and foaming the foam by stirring and / or introducing gas. A step of adding a crosslinking agent and / or a crosslinking initiator to a foamy slurry and introducing the mixture into a mold; and a step of curing the foamy slurry by crosslinking polymerization to form a molded article. In the method for producing a porous sintered body, which comprises a step of drying and sintering the molded body, in the step of introducing the molded body into the mold, bubbles are compressed by pressurization, and the foamed slurry is maintained while maintaining the pressurized state. A porous sintered body which is cured by crosslinking polymerization to control the pore diameter of the porous sintered body.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for producing a porous sintered body of the present invention will be specifically described. A foaming agent is added to a slurry composed of the raw material powder, a dispersion medium, a dispersant, and an organic substance curable by cross-linking polymerization, and foamed by stirring to form a foamy slurry. Here, as the raw material powder, a ceramic raw material powder generally produced by sintering, such as alumina, zirconia, mullite, silica, cordierite, silicon carbide, silicon nitride, aluminum nitride, or a composite thereof is used. Metal powders such as stainless steel, tungsten, and molybdenum, which are generally produced by powder metallurgy, can be used.

As the dispersion medium, a liquid which does not affect the raw material powder can be used. For example, water, ethanol
, Methanol, propanol, acetone, toluene,
Examples include benzene and xylene. The dispersant is not necessarily required, but is appropriately selected and used depending on the raw material powder and the dispersion medium. Organic substances that can be cured by cross-linking polymerization are:
A substance capable of causing cross-linking polymerization by a curing agent and / or a reaction initiator can be used. Although a general surfactant can be used as the foaming agent, it is selected in consideration of the dispersion state of the raw material powder and the interaction with an organic substance which can be cured by cross-linking polymerization.

[0012] Foaming by stirring can be carried out by a method of foaming simply by a gas entrained by stirring or a method of introducing gas into the slurry together with stirring. Foaming can be performed in air, but also in an atmosphere of nitrogen, argon, hydrogen, helium, or the like.
At the time of stirring and foaming, the amount of bubbles introduced is controlled to adjust the porosity of the porous sintered body. After the introduction of the bubbles is completed, it is preferable that the foamed slurry is further stirred under the condition that the bubbles are not introduced to homogenize the pore diameter in the foamed slurry.

After adding and mixing a curing agent to the foamy slurry, the mixture is introduced into a mold placed in a reduced-pressure container or a pressurized container, and bubbles are expanded or compressed under reduced pressure or pressure. After expanding or compressing the foamy slurry to a predetermined volume,
The depressurization or pressurization is stopped, and the slurry is gelled by cross-linking polymerization while maintaining the depressurized or pressurized state, loses fluidity and hardens, is returned to atmospheric pressure, and is demolded to obtain a molded article.

The compact is dried and sintered to form a porous sintered body. The curing agent added here may be any substance that has a function of causing gelation by causing cross-linking polymerization with an organic substance that is added to the slurry and curable by cross-linking polymerization. This includes a polyfunctional crosslinking agent, a reaction initiator, a catalyst, and the like. Here, the volume of the foamed slurry increases or decreases due to the reduced pressure or the increased pressure. This volume, the amount of the introduced bubbles described above, the weight of the raw material powder contained in the slurry, The final porosity of the porous sintered body is determined by the shrinkage ratio at the time of sintering.

[0015] The diameter of the bubbles contained in the foamed slurry increases or decreases due to the reduced pressure or the increased pressure. In turn,
According to this method, the pore diameter of the porous sintered body can be arbitrarily changed and controlled without changing the components and characteristics of the slurry. Note that the change in the pore diameter does not simply follow Boyle's law, but also considers the effect of coalescence of bubbles. That is, a preliminary test is performed in advance, the effect of the characteristics of the slurry on the pore diameter is investigated, and the pore diameter is controlled based on the result. As described above, according to the method for manufacturing a porous sintered body of the present invention, it is possible to easily manufacture a porous sintered body having a controlled pore diameter.

[0016]

An example of controlling the pore diameter by the method for producing a porous sintered body of the present invention will be described below. Note that specific examples or numerical values and conditions such as materials, materials, foaming amounts, pore diameters of porous sintered bodies, porosity of porous sintered bodies, and the like shown in the examples are merely for showing a preferred example. It is not intended to limit the invention. 100 parts by weight of α-alumina powder having an average crystal particle diameter of 0.2 μm as a raw material powder, 0.5 parts by weight of magnesium carbonate as an abnormal grain growth inhibitor, 25 parts by weight of ion exchange water as a dispersion medium, and ammonium polyacrylate as a dispersant 0.75 parts by weight were mixed and mixed for one day with a ball mill. Here, 5 parts by weight of sorbitol polyglycidyl ether was added as an organic substance curable by cross-linking polymerization, and the mixture was sufficiently mixed to obtain a raw material slurry.

To the raw material slurry, 0.25 parts by weight of triethanolamine lauryl sulfate was added as a foaming agent. 630 g of this slurry was taken out and foamed with a stirrer to obtain a foamy slurry. Here, as shown in Table 1, the amount of bubbles introduced by the bubbles was adjusted to change the volume of the foamy slurry. The slurry was further stirred under the condition that no bubbles were introduced to homogenize the bubble diameter. Further, 1.3 parts by weight of iminovirpropylamine as a curing agent was added and mixed. The obtained foamy slurry was poured into a mold placed in a reduced-pressure container or a pressurized container, and the volume was reduced to 1000 cm ² by depressurization or pressurization. Next, it was left for 1 hour while maintaining a reduced pressure or a pressurized state, and after being cured by cross-linking polymerization, returned to the atmospheric pressure, demolded, dried, and sintered at 1650 ° C. for 2 hours to have a porosity of 75%. Was obtained.

The average pore diameter of the porous sintered body was determined by the method described below. The porous sintered body is embedded in a resin, polished and observed with a microscope or the like, and the pore area is determined by image analysis. The number of pores to be measured here is preferably as high as possible in accuracy, but generally it is sufficient to measure 300 or more pores. The pore area obtained here is a cross-section on a plane passing through a part of a substantially spherical pore, and is not the diameter of the pore. Therefore, three-dimensional correction is performed. As a correction method, Jo
The hnson-Saltykov method is used. In the Johnson-Saltykov method,
The pore diameter distribution can be obtained directly from the observed pore area, and the average pore diameter is calculated as the pore diameter that accounts for 50% of the total pore volume in the cumulative pore volume distribution. Table 1 shows the obtained average pore diameters. As shown in Table 1, by making the volume constant by reducing or increasing the pressure, the average pore diameter of the porous sintered body can be easily controlled using the same raw material slurry.

[0019]

[Table 1]

[0020]

As is clear from the examples, according to the method for producing a porous sintered body of the present invention, the same raw material slurry is used, and the steps of stirring and foaming, gelling, drying and sintering are performed. Thus, the present invention has an excellent effect that a porous sintered body having a controlled pore diameter can be easily obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sumie Sakaguchi 30 Soya, Hadano-shi, Kanagawa Toshiba Ceramics Co., Ltd. Inside

Claims (2)

[Claims] 1. A step of preparing a slurry in which a raw material powder and an organic substance which is cured by cross-linking polymerization are dispersed or dissolved in a solvent, adding a foaming agent to the slurry, and foaming by stirring and / or introducing gas. A step of adding a crosslinking agent and / or a crosslinking initiator to the foamy slurry and introducing the mixture into a mold; and a step of curing the foamy slurry by crosslinking polymerization to form a molded article. In the method for producing a porous sintered body, which comprises a step of drying and sintering the molded body, in the step of introducing the molded body into the mold, bubbles are expanded under reduced pressure, and a foamy slurry is maintained while maintaining the reduced pressure state. A method for producing a porous sintered body, characterized in that the pore diameter of the porous sintered body is controlled by curing the porous sintered body through crosslinking polymerization. 2. A step of preparing a slurry in which a raw material powder and an organic substance which is cured by cross-linking polymerization are dispersed or dissolved in a solvent, adding a foaming agent to the slurry, and foaming by stirring and / or gas introduction. A foaming slurry, a step of adding a crosslinking agent and / or a crosslinking initiator to a foamy slurry and introducing the mixture into a mold, and a step of curing the foamy slurry by crosslinking polymerization to form a molded article. And a step of drying and sintering the molded body, wherein in the step of introducing into the mold, bubbles are compressed by pressurization, and the foam is maintained while the pressurized state is maintained. A method for producing a porous sintered body, characterized in that a porous slurry is cured by crosslinking polymerization to control the pore diameter of the porous sintered body.