JP5352809B2 - Ceramic solid-phase foam and method for producing the same - Google Patents

Description

  The present invention relates to a ceramic solid-phase foam and a method for producing the same, and more specifically, a ceramic solid body in which closed pores composed of dense pore walls are present in a ceramic sintered body at a high porosity by utilizing superplasticity. The present invention relates to a phase foam and a method for producing the same.

  Since gas is difficult to transfer heat, a solid containing a large number of closed cells has an excellent heat insulating effect and is suitably used as a heat insulating member. Polymer foams such as polystyrene foam are produced by increasing the temperature to soften polystyrene and at the same time vaporizing the contained foam gas. The foam metal is also produced in the same manner as the polymer foam in that bubbles are introduced into the melted and softened metal except that the production temperature is higher.

  On the other hand, a ceramic material is generally manufactured by sintering at a temperature lower than the melting point of the ceramic material, which is generally called a sintering method. Therefore, the method for producing a foam is completely different from a polymer material or a metal. As a method for producing a ceramic foam, a partial sintering method (Non-Patent Document 1) in which sintering is performed by controlling a molding pressure and a firing temperature during ceramic production, a pore forming agent such as carbon is added, and molding is performed. Then, a pore-forming agent introduction method (Non-patent Document 2) in which the pore-forming agent is scattered and sintered while leaving its traces has been studied. In these methods, open pores that allow easy gas exchange between the inside of the pores and the ambient temperature are formed, so that the surface area per unit volume increases, and the method is used as a catalyst carrier or a gas sensor (Non-patent Document 3).

  However, all of these methods inevitably undergo incomplete sintering because sintering is performed after the introduction of pores. That is, the sintering involves the elimination of the pores, and the porosity is reduced when the sintering is completed. Therefore, in order to maintain the porosity at a high rate, it is necessary to interrupt the sintering in the middle. In addition, when closed pores are introduced into the ceramic foam in order to enhance the characteristics as a heat insulating member, there is a drawback that the porosity is lowered. Furthermore, there is a problem that as the porosity is increased, the bonding between the ceramic particles becomes insufficient, and the mechanical strength is significantly reduced.

  In recent years, much research has been conducted on ceramic foams produced via a liquid phase. For example, after a synthetic resin foam is immersed in a ceramic slurry to attach the ceramic slurry to the synthetic resin foam, the ceramic porous body is dried and fired to thermally decompose or incinerate the synthetic resin foam (Patent Document 1). A mixed powder of silica and other ceramic components such as alumina is ammoniated, and after molding, a siliceous foam (Patent Document 2) that is heated and foamed at a high temperature of about 1650 ° C., binder resin aqueous solution and ceramic A method for producing a ceramic foam by forming a slurry precursor composition with a powder and then heating and drying to a foaming temperature to produce a foamed powder agglomerated molded body and sintering it at a temperature and atmosphere suitable for the ceramic powder material (Patent Document 3).

  However, although these liquid phase methods are easy to introduce bubbles into the precursor slurry solution or sol, the organic matter is scattered at the time of solidifying the slurry, so that the bubbles remain high as independent bubbles. The porosity cannot be maintained. Since pores are excluded during the sintering process, the porosity is inevitably lowered, as in the solid phase method in which sintering is performed after the introduction of bubbles.

  Further, in the case of a polymer material, a metal material, or glass, a foam is produced by heating to a temperature higher than the melting point and introducing bubbles in a molten state. However, ceramics have a remarkably high melting point compared to these materials. For this reason, it is impractical to heat a ceramic used as a refractory to a temperature higher than the melting point to melt the ceramic and introduce bubbles in the molten state, and to apply such a method to porous ceramics. Was practically impossible. Further, ceramic has a low plastic deformability at a temperature below the melting point, and the ceramic cannot be foamed using a foaming agent.

As described above, the conventional ceramic foam is limited to the method of foaming before sintering in order to make the sintering process an essential manufacturing process, and has a high porosity with closed pores composed of dense pore walls. A sintered body could not be produced.
A. Diaz, S. Hampshire, JF. Yang, T. Ohji, and S. Kanzaki, “Comparison of Mechanical Properties of Silicon Nitrides with Controlled Porosities by Different Fabrication Routes”, J. Am. Ceram. Soc., 88 [3 698-706 (2005) R.Barea, MIOsendi, P.Miranzo, and JMFFerreira, “Fabrication of Highly Porous Mullite Materials”, J.Am.Ceram.Soc., 88 [3] 777-779 (2005) SLSuib, “Sorption, catasysis, and separation by design”, Chemical Innovation, 30 [3] 27-33 (2000) JP-A-5-238848 Japanese Patent Laid-Open No. 7-144934 JP 2001-335809 A

  The present invention solves the above-mentioned problems of the prior art, provides a ceramic solid-phase foam having high porosity with closed pores composed of dense pore walls, and makes this ceramic solid-phase foam practical. It is intended to be provided by a method.

  As a result of intensive investigations aimed at solving the above-mentioned problems, the present inventors made a ceramic sintered body foamed in a solid phase after sintering, thereby achieving excellent gas barrier properties and strength characteristics, from a dense pore wall. The present invention has been completed by finding a solid-phase foaming method that can make many closed pores exist.

  In particular, when the ceramic is heated and held at the sintering temperature, the sintered ceramic sintered body develops a superplastic phenomenon, and when this superplasticity is used, a foaming agent that foams at a high temperature such as the sintering temperature is used. Solid-phase foaming is possible in which the encapsulated ceramic is foamed after sintering, and a ceramic solid-phase foam having a high porosity with closed pores composed of dense pore walls can be produced. That is, a ceramic powder is encapsulated with a high-temperature foaming agent to form a molded body. This molded body is sintered to produce a ceramic sintered body with a dense outer skin, and then the ceramic sintered body is held at the sintering temperature. Then, due to the superplastic phenomenon of the ceramic sintered body, the ceramic sintered body is easily foamed in a solid state by the pressure of the gas generated from the encapsulated foaming agent.

  Here, the “dense pore wall” means that the ceramic part (pore wall) surrounding the pores is dense in the ceramic solid foam produced by foaming. That is, it means that the ceramic part which is the outer skin of the solid-phase foam as the sintered molded body is dense, and the ceramic part between the pores in the solid-phase foam is also dense. The “dense” depends on the molding pressure when the ceramic matrix powder and the foaming agent are integrally molded, but the relative density of the ceramic portion of the pore wall is at least 90%, preferably 95% or more, more preferably Means 98% or more.

  Therefore, the present invention is a ceramic solid-phase foam, wherein the ceramic solid-phase foam has closed pores composed of dense pore walls.

  In the ceramic solid phase foam of the present invention, as described below, the ceramic matrix powder and the foaming agent included in the ceramic matrix powder are integrally molded, and the molded body is sintered and foamed. The porosity of the closed pores can be controlled to a desired porosity within a wide range, for example, in the range of 70 to 80% or less. However, in order to enjoy the effects of the airtightness, heat insulation, and reliability provided by the ceramic solid phase foam of the present invention, the porosity of the closed pores composed of dense pore walls is 5 to 60%. In view of high temperature strength, it is more preferably 30 to 50%.

  The present invention also includes a step of encapsulating a foaming agent in the ceramic matrix powder, a step of integrally molding the ceramic matrix powder and the foaming agent to obtain a molded body, and holding the integrally molded body at the sintering temperature of the ceramic matrix. Thus, a method for producing a ceramic solid-phase foam comprising the steps of sintering a ceramic matrix and then foaming a foaming agent in the sintered ceramic sintered body. The foaming agent is preferably a foaming agent that is preformed or solidified using an organic binder.

  The present invention sinters a ceramic molded body to form a ceramic having a dense pore wall, and at the same time, utilizes the superplastic phenomenon of the ceramic and the gas pressure of the gas generated from the internal high-temperature foamed material, thereby making the dense pore wall It is possible to produce a ceramic foam having the closed pores made of the above at a high porosity in the solid phase. In particular, since the pore walls are dense, it is possible to provide a ceramic solid-phase foam that is excellent in gas barrier properties and excellent in strength and airtightness and high reliability. Moreover, since the ceramic solid-phase foam of this invention can be manufactured under the atmospheric pressure and the temperature of the ceramic sintering temperature vicinity, it is a highly practical manufacturing method. For this reason, it can use suitably as heat insulation parts, such as an engine member and an industrial furnace member, as a reliable heat insulation material with a large specific strength. In addition, as a lightweight material with excellent high-temperature strength, air-tightness at high temperatures, such as thermal insulation members of spacecrafts that are exposed to temperatures around 1200 ° C when entering the atmosphere, and reactor wall members that are highly airtight and reliable Innovative materials can be provided in fields where both properties and thermal insulation properties are required.

  In particular, in industrial furnaces, when substances containing chlorine are burned, the generation of dioxins becomes a problem, and these substances need to be burned at a high temperature of 1000 ° C. or higher. However, the heat insulating material using the conventional ceramic porous body has an infinite number of open pores, and vaporized components including chlorine are trapped in the open pores. For this reason, when the temperature of the heat insulating material is lowered and maintained at a temperature of 1000 ° C. or less, for example, dioxins are generated by chlorine trapped in the open pores of the heat insulating material, or the generated dioxins are discharged to the outside. It was difficult to control. However, since the ceramic solid-phase foam of the present invention has a dense outer skin, not only the heat insulating parts using the ceramic solid foam but also the toxic poison reaction vessel can suppress trapping of the raw material and suppress the outflow of the product. It can be said that it is an airtight material that can cope with zero emission that can completely control the generated product.

  Furthermore, the ceramic porous body that has been put to practical use has the disadvantages that since most of the pores are open pores, there is no sound insulation effect and the electrical characteristics are easily affected by humidity in the atmosphere. The ceramic solid phase foam of the present invention is characterized in that the pores are closed pores, and not only as an outer wall as a sound insulation component having a high sound insulation effect, but also as an engine member requiring heat insulation and air tightness, and It can be used as a porous electrical component whose electrical characteristics hardly change with humidity.

It is a photograph which shows the shape of a ceramic solid-phase foam when a molded object is heated and hold | maintained at 1600 degreeC for 8 hours ((a) Example 1, (b) Example 2, (c) Example 3). It is a figure which shows the retention time dependence of the foaming height of a ceramic solid-phase foam when Example 1 is heat-held at 1600 degreeC. It is the photograph which shows the shape of the ceramic solid-phase foam of Examples 5-6 which made it foam after mounting the foaming agent pellet cut into 3 mm square on a ceramic matrix by various patterns ((a) Example 5, (B) Example 6). It is a photograph which shows the shape of the ceramic solid-phase foam of Example 7 using the patterned sheet | seat which patterned the foaming agent in the shape of the solitary island. It is a photograph which shows the cross-sectional shape of the ceramic solid-phase foam of Example 7 using the patterned sheet | seat which patterned the foaming agent in the shape of the solitary island. It is a photograph which shows the shape of the ceramic solid-phase foam of Example 8 using the patterned sheet | seat which patterned the foaming agent in the shape of a continuous curve.

  The present invention will be described in detail below.

  The ceramic solid-phase foam of the present invention is a ceramic sintered body containing a foaming agent that foams at a high temperature to sinter a ceramic sintered body having a dense pore wall, and then sintered at a sintering temperature. Since the body is held and the superplastic phenomenon of the ceramic sintered body and the pressure of the gas generated from the foaming agent are utilized, closed pores composed of dense pore walls have a high porosity. The porosity of the closed pores can be 5 to 60% by controlling the type and amount of the foaming agent to be included in the ceramic matrix. In particular, it is possible to obtain a ceramic solid-phase foam having a very high porosity of 30 to 50%, which has not been realized so far with ceramic foam.

  The ceramic matrix uses one or more of alumina, zirconia, magnesia, silica, titania, etc., or composite ceramics such as sialon, mullite, cordierite, etc., which develop a superplastic phenomenon by maintaining the sintering temperature. can do. In order to improve the characteristics of these ceramics, ceramics selected from yttria, calcia, magnesia, rare earth oxides such as scandium oxide, ytterbium oxide, etc. as the second and third components are made into a ceramic matrix. In contrast, a matrix added in an amount of 10 mol% or less can be used. For example, 3 mol% yttria-stabilized zirconia (hereinafter referred to as “3YSZ”) can be preferably used.

  Further, as an aid for facilitating the superplastic phenomenon of the ceramic solid phase foam, it is selected from the group consisting of silica, alumina, copper oxide, titania, manganese oxide, magnesia, zirconia, yttria stabilized zirconia, germanium oxide, One or more ceramic components different from the matrix can be contained in an amount of 10% by weight or less based on the total amount of the matrix. By adding a ceramic component different from these ceramic matrix components, it is possible to suppress the grain growth of the ceramic during sintering, so that the superplastic phenomenon can be promoted and the foaming performance can be enhanced.

  The method for producing a ceramic solid phase foam of the present invention comprises a step of encapsulating a foaming agent in a ceramic matrix powder, a step of integrally molding the ceramic matrix powder and the foaming agent to obtain a molded body, and an integrally molded molded body. Heating and holding to the sintering temperature of the ceramic matrix, thereby sintering the ceramic matrix and then foaming the foaming agent in the sintered ceramic sintered body.

  The ceramic matrix uses one or more of alumina, zirconia, magnesia, silica, titania, etc., or composite ceramics such as sialon, mullite, cordierite, etc., which develop a superplastic phenomenon by maintaining the sintering temperature. can do. In order to improve the characteristics of these ceramics, ceramics selected from yttria, calcia, magnesia, rare earth oxides such as scandium oxide, ytterbium oxide, etc. as the second and third components are made into a ceramic matrix. In contrast, a matrix added in an amount of 10 mol% or less can be used. In addition, as an aid for facilitating the superplastic phenomenon of the ceramic solid phase foam, it is selected from the group consisting of silica, alumina, copper oxide, titania, manganese oxide, magnesia, zirconia, yttria stabilized zirconia, germanium oxide and the like. One or more kinds of ceramics different from the matrix can be contained at 10% by weight or less with respect to the total amount of the matrix to promote the superplastic phenomenon and enhance the foaming performance.

The foaming agent used in the production method of the present invention is preferably a molded body that is preformed or solidified using an organic binder. That is, in the present invention, the ceramic powder is held at the sintering temperature and then sintered, and then held at the sintering temperature, thereby utilizing the superplastic phenomenon of the ceramic sintered body to hold the sintered temperature. The ceramic sintered body is foamed in a solid state by the pressure of the gas generated from the foaming agent. For this reason, in order to increase the pressure of the generated gas, the foaming agent preferably has a size as a molded body obtained by solidifying the powder. After molding a single molded body at a predetermined position in the ceramic matrix or disposing a plurality of small molded bodies dispersed at a predetermined position in the ceramic matrix, the molded body is integrally formed with the ceramic powder. can do. Furthermore, after a small molded body is uniformly dispersed in the ceramic matrix powder, it can be integrally formed with the ceramic powder. Therefore, if the size of the solidified foaming agent has a volume of, for example, about 0.003 cm ^3, it can be suitably used in the method of the present invention. Moreover, as an organic binder, methyl cellulose and polyvinyl alcohol (PVA) can be used, for example. The shape of the molded body is not particularly limited, and the foam may be a whisker or fiber molded body.

  The foaming agent material should be a foaming agent that does not foam at the stage of sintering the ceramic powder molded body but foams at the stage of maintaining the ceramic sintered body at the sintering temperature. As such a foaming agent, one or more selected from silicon carbide, carbonates such as barium carbonate and sublimable solids such as vanadium chloride can be used. In particular, silicon carbide is preferable because the ceramic material (silica) produced by the decomposition reaction of the foaming agent (SiC) increases the superplastic deformation ability of the matrix, as will be described later. The amount of the foaming agent used depends on the porosity of the target closed pores of the ceramic solid phase foam, but is preferably 2 to 30 parts by weight, more preferably 3 to 30 parts by weight with respect to 100 parts by weight of the ceramic matrix. 10 parts by weight.

  A temperature suitable for sintering the ceramic matrix can be adopted as the temperature to be heated and held at the sintering temperature. That is, a suitable temperature range is selected depending on the ceramic composition as the matrix to be used and the particle size of the powder. In addition, the time for heating and holding at the sintering temperature depends on the amount of foaming agent used and the superplastic properties of the ceramic matrix, but is preferably 1 to 24 hours, more preferably 2 to 10 hours. . Foaming in the present invention is performed in a cycle of generating gas from the foaming agent, increasing the internal pressure in the sintered body, decreasing the internal pressure (foaming driving force) due to expansion of the outer skin of the sintered body, and ending foaming. Gas generation from the foaming agent is completed within about 6 hours of holding time at the sintering temperature, but superplastic deformation of the ceramic sintered body takes time, and the holding time at the sintering temperature is about 24 hours. This is because the deformation may continue until.

The ceramic solid-phase foam of the present invention is obtained by sintering a ceramic powder to produce a ceramic sintered body having a dense pore wall, and then holding the ceramic sintered body at a sintering temperature. Due to the plastic phenomenon, the ceramic sintered body is foamed in the solid state by the pressure of the gas generated from the high-temperature foaming agent. That is, the ceramic solid-phase foam of the present invention increases the internal pressure of a ceramic sintered body having a dense pore wall, using a gas pressure such as CO gas or CO ₂ gas generated by an oxidative decomposition reaction of the foaming agent as a driving force, It is formed by expanding the outer skin of a ceramic sintered body in a superplastic state.

Taking silicon carbide (SiC) as an example of the foaming agent, the decomposition reaction of SiC is considered to take the following reaction depending on the surrounding oxygen concentration.
Oxidizing atmosphere SiC + 3 / 2O ₂ → SiO ₂ (s) + CO (g) (1)
Reducing atmosphere SiC + O ₂ → SiO (G) + CO (g) (2)
In an oxidizing atmosphere, since 1 mol of CO is generated from 1.5 mol of oxygen, the sintered body does not foam. However, in a reducing atmosphere (under reduced pressure), 2 mol of gas is generated per 1 mol of oxygen, and when the sintering is completed, the surface of the ceramic sintered body is densified and a sealed state is formed. The expanded gas expands the ceramic sintered body in the superplastic state, so that the ceramic sintered body is foamed.

  The pore inner wall obtained by foaming SiC as a foaming agent was covered with a glassy white solid and was found to be an amorphous halo showing a broad peak according to X-ray diffraction. Therefore, it is suggested that the vaporized product at the time of foaming solidifies when the temperature is lowered, and the inside of the pores is depressurized. Since the thermal conductivity of the gas increases depending on the gas molecular weight, high heat insulation can be expected up to the temperature at which the solidified component is re-vaporized.

  In addition, using the ceramic solid phase foam of the present invention, in order to produce heat insulation parts, sound insulation parts, electrical parts, etc., which are desired applications, a foaming agent is included so as to have a predetermined size and shape after foaming. Determine the dimension and shape of the ceramic matrix powder molding. In addition, the ceramic matrix powder molded body can be produced by sintering and foaming in a molding die having a predetermined size and shape of these parts.

  EXAMPLES The present invention will be specifically described below using examples, but the examples are illustrative of the present invention and do not limit the scope of the present invention.

Example 1
3 mol% yttria stabilized zirconia (3YSZ) was used as the ceramic matrix and silicon carbide was used as the blowing agent. Silicon carbide powder (Ibiden Co., Ltd., β-SiC, Grade-UF) 0.5 g was charged into a 10 mm diameter molding machine, and uniaxially pressed at a normal pressure of 30 MPa at a pressure of 30 MPa, diameter 10 mm, thickness 0 A 05 mm pellet was obtained. Next, 3 g of 3YSZ (manufactured by Tosoh Corporation, product number: TZ-3Y) is divided into two groups of 2 g, and 3YSZ powder, SiC molded body, and 3YSZ powder are placed in this order in a molding machine having a diameter of 20 mm. Uniaxial pressure molding was performed at a pressure of 30 MPa for 1 minute, and then hydrostatic pressure was applied at 200 MPa for 1 minute to obtain a molded body having a diameter of 20 mm and a thickness of 5 mm. The molded body was heated to 1600 ° C. at a temperature rising rate of 800 ° C./h in the air using a high-speed heating furnace (Kantal super furnace), and held at this temperature for 2 to 8 hours. A foam was obtained. The obtained ceramic solid phase foam was cooled to room temperature at 300 ° C./h.

About the obtained ceramic solid-phase foam, the following tests were done and the characteristic was evaluated.
(1) Foaming performance Using a scale, the difference between the thickness of the ceramic solid foam and the thickness of the molded body before sintering was measured, and the foaming performance was evaluated using this as the foaming height.
(2) Mechanical properties at high temperature Investigate whether the ceramic solid foam breaks when a hydrostatic pressure of 1600 ° C. and 195 MPa is applied in an argon atmosphere using a hot isostatic pressing device. did.
(3) Measurement of thermal conductivity The thermal conductivity based on the laser flash method was measured at room temperature using a thermal conductivity measuring device (manufactured by Netzsch, Germany, model number: LFA457).
(4) Measurement of porosity and density The bulk density of the ceramic solid phase foam was measured according to the Archimedes method. For example, when the bulk density of the ceramic solid foam is 4.8 g / cm ³ and the theoretical density of the ceramic described in the known literature is 6.0 g / cm ³ , the relative density is 4.8 / 6.0 = 80%, so the porosity is 100-80 = 20%.

FIG. 1A shows the shape of a ceramic solid foam when the molded body is heated and held at 1600 ° C. for 8 hours, and FIG. 2 shows the foam height of the ceramic solid foam when heated and held at 1600 ° C. The retention time dependency of the length is shown. Although the foam height after holding for 2 hours is 3.6 mm, the foam height after holding for 8 hours is 5.1 mm, and it can be seen that foaming has progressed due to the holding after completion of sintering of the ceramic. In addition, the density of the outer skin (pore wall) portion corresponding to the solid foam foam shell in FIG. 1 (a) is 6.05 g / cm ³ , and the relative density of the outer skin portion is 99% or more. It shows that the outer skin part is dense. That is, the solid foam of Example 1 shows that the outer skin swells due to gas pressure after densification after sintering. Moreover, the density of the solid-phase foam after holding for 8 hours was 4.39 g / cm ³ , and the porosity was 29.3%. Although the temperature was raised to the sintering temperature of 1600 ° C. while applying a hydrostatic pressure of 195 MPa using argon as a medium, the ceramic solid foam maintained the shape and did not break. Therefore, ceramic solid foams have good high temperature mechanical properties.

Example 2
In the ceramic solid phase foam of the present invention, foaming uses the internal pressure of the gas generated by the oxidative decomposition reaction of the foaming agent as the driving force, but when heated to the sintering temperature in the atmosphere, the oxidative decomposition reaction of the foaming agent is It is considered that the process proceeds even when the temperature is raised to the sintering temperature. Therefore, during the temperature rise to the sintering temperature of 1600 ° C., the atmosphere in the furnace was argon gas, the atmosphere in the furnace was switched to air when held at the sintering temperature, and the heating and holding time at the sintering temperature was 8 hours. A ceramic solid phase foam was produced in the same manner as in Example 1 except that. FIG. 1 (b) shows the shape of the ceramic solid phase foam of Example 2. The foaming height after holding for 8 hours was 5.5 mm, and the foaming height increased compared with the temperature rise and maintenance in the atmosphere (air) of Example 1, and the porosity of the closed pores was also 38. It has increased to 9%. Therefore, in order to suppress the oxidative decomposition of the foaming agent when raising the temperature to the sintering temperature, the atmosphere in the furnace is made an inert gas, thereby improving the foaming performance of the ceramic solid foam and increasing the porosity of the closed pores. Can be improved.

Example 3
Example 1 except that 3YSZ in which 5 wt% of SiO ₂ was added to 3 mol% yttria stabilized zirconia (3YSZ) was used as the ceramic matrix, and the heat holding time at the sintering temperature was 8 hours. In the same manner, a ceramic solid-phase foam was produced. FIG. 1 (c) shows the shape of the ceramic solid phase foam of Example 3. The foaming height after holding for 8 hours is 6.5 mm, and the foaming height is higher than that of Example 1 in which the ceramic matrix is 3YSZ alone. The porosity of the closed pores was 42.2%. This indicates that the addition of 5% by weight of SiO ₂ functions as an auxiliary agent that makes it easier to develop the superplastic phenomenon of the ceramic solid phase foam.

Example 4
As foaming agents, 14 pieces of compacted foaming agent (size: 0.003 cm ³ ) of about 0.01 g are divided into three groups of five, four and five, and these are sandwiched between 1 g of 3YSZ powder. Formed, ie, 3YSZ powder / 5 foaming agent / 3YSZ powder / 4 foaming agent / 3YSZ powder / 5 foaming agent / 3YSZ powder in this order and uniaxially pressed to obtain a molded body A ceramic solid foam was produced in the same manner as in Example 1 except that the heating and holding time at the sintering temperature was 8 hours. The obtained ceramic solid-phase foam had a closed porosity of 7.8% and a relative density of 92.2%. The thermal conductivity of this solid foam was 2.6 W / m · K. For comparison, the thermal conductivity of a ceramic sintered body with a relative density of 100% produced under the same conditions was 3.72 W / m · K. Therefore, the ceramic solid phase foam of the present invention has a thermal conductivity of 70% with respect to a dense ceramic sintered body, and can reduce the thermal conductivity more than a decrease in relative density.

Example 5 and Example 6
3 mol% yttria stabilized zirconia (3YSZ) was used as the ceramic matrix and silicon carbide was used as the blowing agent. Silicon carbide powder (Ibiden Co., Ltd., β-SiC, Grade-UF) 0.5 g was charged into a 10 mm diameter molding machine, and uniaxially pressed at a normal pressure of 30 MPa at a pressure of 30 MPa, diameter 10 mm, thickness 0 A 05 mm pellet was obtained. This pellet was cut into small pieces (weight: about 0.07 g, size: 0.00045 cm ³ ) using a razor. Carved. Next, 3 g of 3YSZ (manufactured by Tosoh Corporation, product number: TZ-3Y) was divided into 2 groups of 2 g, and 3YSZ powder, SiC pieces, and 3YSZ powder were put into a molding machine having a diameter of 20 mm in this order. A plurality of SiC pieces were positioned by tweezers or the like so as to form a pattern on 3YSZ. Thereafter, in the same manner as in Example 1, ceramic solid phase foams of Examples 5 and 6 were obtained by uniaxial pressing, hydrostatic pressing, heat treatment, and cooling. As shown in FIGS. 3A and 3B, a plurality of closed pores were generated in the foam at the position where the SiC piece was placed.

Example 7
In order to control the position of the foaming agent, a 3YSZ sheet was prepared, and the foaming agent was patterned and placed thereon. First, a methylcellulose aqueous solution (3% by weight) as an organic binder and 3YSZ powder were mixed to prepare a mud (slurry), which was stretched with a glass rod and dried to prepare a 3YSZ sheet. Next, a β-SiC powder, which is a foaming agent, is similarly made into a slurry, and a copper plate on which a pattern is formed by extracting a desired place where the slurry-like β-SiC foaming agent is fixed on a 3YSZ sheet. After pouring on a mask (thickness 0.2 mm) and stretching, the mask was removed and dried. In this manner, a patterned sheet was produced in which β-SiC, which is a foaming agent, was patterned on a 3YSZ sheet into a solitary nodule of 3 × 3 = 9 pieces with a height of 0.2 mm. Next, the patterned sheet is cut into a circular shape, put into a molding machine having a diameter of 20 mm in the order of 3YSZ powder, patterned sheet, 3YSZ powder, patterned sheet, and 3YSZ powder, and uniaxially pressed in the same manner as in Example 1. The ceramic solid phase foam shown in FIG. 4 was obtained by molding, hydrostatic pressure, heat treatment, and cooling. As shown in FIG. 4, this ceramic solid phase foam has isolated closed pores corresponding to the arranged SiC pattern, and, as is clear from the cross section of the cut sample shown in FIG. In the body, not only the surface but also closed pores corresponding to the SiC pattern are uniformly generated inside.

Example 8
A ceramic solid phase foam shown in FIG. 6 was obtained in the same manner as in Example 7 except that the extraction shape of the copper plate mask was changed to an inverted S-shaped continuous curve.

  Therefore, by disposing the foaming agent in a desired pattern, it is possible to form a ceramic solid-phase foam having a plurality of independent closed pores that may exist in the interior or continuous tubular closed pores. Since these ceramic solid-phase foams can be formed in one step without cutting, there are great industrial advantages.

Example 9
Alumina added with a superplasticity imparting agent was used as a ceramic matrix, and silicon carbide was used as a foaming agent. Silicon carbide powder (Ibiden Co., Ltd., β-SiC, Grade-UF) 0.5 g was charged into a 10 mm diameter molding machine, and uniaxially pressed at a normal pressure of 30 MPa at a pressure of 30 MPa, diameter 10 mm, thickness 0 A 05 mm pellet was obtained. On the other hand, alumina (Sumitomo Chemical Co., Ltd., product number: AKP-30) powder as a matrix was wet mixed with 10 mol% of 3YSZ as a superplasticity imparting agent using ethanol as a medium. 4 g of the obtained mixed powder was divided into 2 groups each having 2 g, and the mixed powder, the SiC molded body, and the mixed powder were placed in this order in a molding machine having a diameter of 20 mm. A ceramic solid phase foam was obtained by hydrostatic pressure, heat treatment, and cooling. The density of the obtained solid-phase foam was 3.77 g / cm ³ and the porosity was 10%.

Example 10
A ceramic solid phase foam was obtained in the same manner as in Example 9 except that 30 mol% of magnesia was wet mixed as a superplasticity imparting agent. The density of the obtained solid-phase foam was 3.30 g / cm ³ and the porosity was 15%.

In addition, Examples 9 and 10 using alumina as a ceramic matrix have higher high-temperature strength than Examples 1 to 6 using 3 mol% yttria stabilized zirconia (3YSZ) as a matrix. It was also confirmed that the strength in a humid atmosphere was high.

  The ceramic solid-phase foam of the present invention is a ceramic solid-phase foam having high gas barrier properties, high airtightness and high reliability. For this reason, in addition to reliable heat insulating materials, lightweight materials with excellent high-temperature strength, airtight materials that can suppress the trapping of raw materials and suppress the outflow of products. It can be used as a porous electrical component that is difficult to perform. In addition, since the ceramic solid-phase foam of the present invention can be produced at a temperature close to the sintering temperature of the ceramic at atmospheric pressure, it is a highly practical production method and has high industrial applicability. .

Claims (14)

It is a ceramic solid-phase foam, and the ceramic solid-phase foam is composed of a dense pore wall , an isolated island, a solitary island nodule in which a plurality of isolated islands are uniformly dispersed, or closed pores patterned in a continuous curve shape. A ceramic solid phase foam characterized in that it has a porosity of 5 to 60% , thereby blocking gas permeation. Is a 30-50% porosity of closed pores, claim 1 ceramic solid foam according. Matrix of the ceramic solid foam, alumina, zirconia, magnesia, silica, titania, sialon, is one or more ceramic selected from the group consisting of mullite and cordierite, ceramic solid of Claim 1 or 2, wherein Phase foam. The ceramic solid phase according to any one of claims 1 to 3 , wherein the matrix of the ceramic solid phase foam further contains one or more ceramics selected from the group consisting of yttria, calcia, magnesia and rare earth oxides. Foam. The matrix of the ceramic solid foam is further selected from the group consisting of silica, alumina, copper oxide, titania, manganese oxide, magnesia, zirconia, yttria stabilized zirconia, germanium oxide, and one or more ceramics different from the matrix The ceramic solid-phase foam according to any one of claims 1 to 4 , comprising: Insulation parts, sound insulation parts or electrical components rich in airtightness with ceramic solid foam of claim 1 to 5, wherein. A sheet containing a ceramic matrix powder is prepared, and a foaming agent is patterned and placed in a solitary island nodule or a continuous curve in which a plurality of solitary islands are uniformly dispersed , and the foaming agent is placed in the ceramic powder. A step of encapsulating ceramic matrix powder and a preformed or solidified foaming agent using an organic binder to obtain a molded body, and the integrally molded molded body at the sintering temperature of the ceramic matrix A method for producing a ceramic solid-phase foam, comprising: heating and holding, thereby sintering a ceramic matrix, and then foaming a foaming agent in the sintered ceramic sintered body. The method for producing a ceramic solid phase foam according to claim 7 , wherein the ceramic matrix is one or more ceramics selected from the group consisting of alumina, zirconia, magnesia, silica, titania, sialon, mullite and cordierite. The method for producing a ceramic solid phase foam according to claim 7 or 8 , wherein the ceramic matrix further contains at least one ceramic selected from the group consisting of yttria, calcia, magnesia and rare earth oxides. The ceramic matrix further comprises one or more ceramics selected from the group consisting of silica, alumina, copper oxide, titania, manganese oxide, magnesia, zirconia, yttria stabilized zirconia, germanium oxide and different from the matrix. Item 10. A method for producing a ceramic solid foam according to any one of Items 7 to 9 . The method for producing a ceramic solid-phase foam according to any one of claims 7 to 10 , wherein the foaming agent is at least one selected from the group consisting of silicon carbide, carbonates, and sublimable solids. The method for producing a ceramic solid-phase foam according to any one of claims 7 to 11 , wherein the time for heating and holding at the sintering temperature is 1 to 24 hours. The method for producing a ceramic solid phase foam according to claim 12 , wherein the time for heating and holding at the sintering temperature is 2 to 10 hours. The method for producing a ceramic solid phase foam according to any one of claims 7 to 13 , wherein the temperature is raised to a sintering temperature in an inert gas atmosphere, and heating and holding at the sintering temperature is performed in the air.