JP5555646B2 - Ceramic porous heat insulating material and method for producing the same - Google Patents

Description

  The present invention relates to a ceramic porous heat insulating material having a partition wall structure inside a macropore that can be used at a high temperature, and a method for producing the ceramic porous heat insulating material.

  Conventionally, various methods have been proposed as a method for producing a ceramic heat insulating material that can be used at high temperatures. Among these methods, as the most industrialized method, a heat insulating material produced by melting ceramics at a high temperature and solidifying the obtained fibrous ceramic fiber with a binder is known. However, in this method, since it is necessary to melt the material and process it into a fiber shape, the materials that can be adopted are mainly limited to low melting point materials (mainly alumina and silica). Therefore, the heat insulating material obtained by this method has a problem that the usable temperature is low.

In addition, insulation materials made by solidifying ceramic fibers are inferior in mechanical properties. Therefore, methods such as combining fibers with different materials and diameters, and improvements such as three-dimensional fiber weaving have been made. (See, for example, Patent Documents 1 and 2).
In addition, various proposals have been made to solve the problem of the heat insulating material produced by solidifying the fiber. For example, a heat insulating material produced by adding a foaming agent to a slurry made of ceramic powder and a dispersion medium (for example, water), introducing a large amount of pores into the slurry, and solidifying (see Patent Document 3), Furthermore, there exists a proposal about the heat insulating material (refer patent document 4) produced by making a foam independently, adding to a slurry in the state which prepared the shape of the foam, and solidifying.

Moreover, the method of producing the porous body by producing the gel containing siloxane and drying and baking a gel is known (refer patent documents 5 and 6). However, according to these methods, it is possible to uniformly impart a very fine pore diameter, but the material is limited to silica, and a structural member having a size required as a heat insulating material can be produced. There is a problem that it is difficult and the range of use as a heat insulating material is limited.
As a method for solving such problems, ceramic raw material powder is dispersed in water to prepare a slurry, frozen in one direction to form unidirectional ice in the ceramic, and sublimated by freeze-drying this ice. A porous ceramic body with a high handling strength and a communicating hole is produced by adding a gelling agent and freezing water retained in the gel body (see Patent Document 7). A method (see Patent Document 8) is proposed.

  Unlike conventional methods, these methods can be applied to various materials, have excellent shape imparting properties, and additionally use water as a pore forming means, so that harmful gases generated during production are also present. There is almost no manufacturing method in terms of cost and environment, and industrialization is expected. However, considering that these methods are applied to a means for producing a heat insulating material, the resulting porous body has communication holes, and thus has the following problems. That is, heat and gas pass through the heat insulating material, resulting in inferior heat insulating performance, and high resistance to stress from the same direction as the communication hole, but macroscopic pores are continuous in the orthogonal direction. Therefore, when practical use is assumed as a heat insulating material that is a structural member, there is a problem that high strength cannot be expected.

JP 2002-275747 A JP-A-6-143469 JP-A-5-170571 JP 2004-75444 A JP-A-8-73210 JP 2006-241275 A JP 2001-192280 A JP 2008-201636 A

  The above-described conventional technology specifically discloses application to a heat insulating material, but ceramic heat insulating materials obtained by these techniques are not sufficient depending on the purpose of use, and as described below, Each had room for improvement. Patent Documents 1 and 2 described above disclose that a heat insulating material that can be used under severe conditions can be manufactured by optimizing the size and structure of the ceramic fiber. However, there is a problem that a process for forming a fiber is necessary, and there is a risk of contamination in the apparatus due to dropping of the fiber or the like during the use of the product, and mixing into the product.

  Further, Patent Documents 3 and 4 disclose that bubbles are introduced into ceramic slurry so that independent pores exist in the fired ceramic. However, in Patent Document 3, since sodium silicate or sodium aluminate is used as a starting material, soda remains even if a leaching process is performed, so that it is difficult to use at high temperatures. Further, Patent Document 4 does not describe the material of ceramics, but discloses high characteristics as a heat insulating material. Certainly, this method is expected to be applied to various materials, but there are some industrial problems such as bonding of bubbles by adjusting the size of bubbles in advance, and dispersion of bubbles in slurry. Therefore, it is hard to say that this technology can be industrialized immediately.

  On the other hand, in Patent Document 5, it is possible to produce particles mainly composed of silica having fine pores, and in Patent Document 6, it is disclosed that a porous body having fine pores up to a bulk shape can be produced. Has been. However, since the materials described in Patent Documents 5 and 6 are mainly composed of silica, the melting point is 1,726 ° C. even with high-purity silica. Therefore, the techniques of Patent Documents 5 and 6 are used. The usable temperature of the heat insulating material produced in this manner is expected to be 1,500 ° C. or lower, and there is a problem that the usable temperature is low in the use as a ceramic heat insulating material.

  Furthermore, the manufacturing method of the ceramic porous body described in Patent Documents 7 and 8 can be expected to be applied to various materials as in Patent Document 4. Moreover, in the technique described in patent document 8, since it is possible to make a porosity to 99%, it can be said that it is a technique useful for manufacture of a heat insulating material. However, in any method, since a structural feature is to provide a macroporous communication hole, heat and gas easily pass through the heat insulating material. This is extremely undesirable.

  Therefore, the object of the present invention is to have a low thermal conductivity as a heat insulating material while maintaining the strength required for a heat insulating material as a structural material while being a ceramic porous body easily obtained by utilizing the freezing phenomenon of water. However, an object of the present invention is to provide a ceramic porous heat insulating material that can be used at a higher temperature than conventional ones and has excellent heat and gas barrier properties. Furthermore, the object of the present invention is to use a material such as zirconia that exhibits a high melting point, a material that is conventionally said to be difficult to produce a heat insulating material (for example, boron nitride), and carbon as a material. It is an object of the present invention to provide a manufacturing technique capable of easily and inexpensively manufacturing a ceramic porous heat insulating material that realizes excellent characteristics that are not present in the past.

  The above object is achieved by the present invention described below. That is, the present invention is obtained by a gelation freezing method in which a gel body made from a material containing a ceramic raw material powder and a gelling agent solution is frozen and ice crystals formed at the time of freezing are used as a pore source. In addition, the present invention provides a ceramic porous heat insulating material characterized by being a porous ceramic having a partition structure in which a large number of node-shaped partition walls are formed inside cylindrical macropores derived from a gelling agent.

The following are mentioned as a preferable form of the said invention.
The partition structure is formed by forming a film made of the same material as the macropores in a cylindrical macropore having an inner diameter of 10 to 300 μm, and the membrane has a thickness of 1 to 10 μm and has macropores. The above-described structure has a structure in which a large number of node-like partition walls are formed with the interval between the membranes being 10 to 100% of the inner diameter of the macropores. The ceramic porous heat insulating material is mentioned. The porosity of the porous ceramics is 50 to 99%, and the macropores have a cylindrical shape with an inner diameter of 10 μm to 300 μm, and the air permeability is 1 × 10 ⁻²⁰ to The ceramic porous heat insulating material is 1 × 10 ⁻¹² m ² . Moreover, said ceramic porous heat insulating material in which the internal diameter of the said macropores exists in the range of 10-300 micrometers which freezes the said gel body at -10 degrees C or less is mentioned. In addition, the ceramic porous heat insulating material may include at least one selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, boron nitride, cordierite, and carbon.

  Furthermore, the present invention provides, as another embodiment, a method for producing a ceramic porous heat insulating material for producing a porous ceramic having a partition wall structure by using a gelation freezing method, comprising a ceramic raw material powder, a gelling agent A gelation step for obtaining a gel body from a material containing a lysate, a freezing step for freezing the gel body to obtain a frozen body, and a drying obtained by removing ice from the frozen body obtained in the freezing step A drying / firing step for firing the body, the gelling step including the gelling agent, and an organic compound or an inorganic compound that causes a freezing point depression of the gel body, and the freezing step during freezing. When the water in the gel body is cooled and ice crystals serving as the pore source are formed, the cylindrical macro ice crystals derived from the gelling agent, and the freeze-concentration and gel bodies are contained inside the macro ice crystals. Many nodular bulkheads formed by freezing point depression Te to obtain a frozen body having a partition wall structure, with the drying-calcination step, to remove the ice from the frozen bodies, to provide a method of manufacturing a ceramic porous insulation material, characterized in that to obtain a porous ceramic.

  As a preferred form of the production method of the present invention, the organic compound or inorganic compound that causes the freezing point depression of the gel body is an acrylamide polymer, alginic acid polymer, polyethyleneimine polymer, methylcellulose polymer, poly An acrylic acid polymer, a polycarboxylic acid polymer, polyethylene glycol, polyprene glycol, ethylene glycol, at least one selected from the group consisting of lower alcohols having 1 to 3 carbon atoms, nitrates and chloride salts, and The compound may be contained so as to be 0.1 to 13% by volume (0.1 to 15.0% by mass when converted to mass%) with respect to the ceramic raw material powder.

  The porous ceramic characterizing the present invention has a bulkhead structure in which a large number of node-shaped bulkheads are formed in a state of having cylindrical macropores and being erected on the inner walls of the macropores. . Such a barrier rib structure is a unique structure that has not been conventionally used, and is a fine structure that is difficult to pass heat and gas and is useful as a heat insulating material. Therefore, an excellent ceramic porous heat insulating material can be provided. This porous ceramic is an organic compound or an inorganic compound that causes a freezing point depression in a gelation freezing method using ice crystals generated when freezing a mixture of a ceramic raw material powder and a gelling agent solution as a pore source. A new partition wall in which a large number of partition walls formed from the above-mentioned compound that causes a freezing point depression are provided inside a cylindrical macropore formed from a gelling agent by containing the above in the raw material A ceramic porous body having a structure can be easily obtained.

It is a figure of the SEM photograph of the cross section of the ceramic porous body of Example 1 of this invention. It is a figure of the SEM photograph of the cross section of the ceramic porous body of Example 2 of this invention. It is a schematic diagram which shows the partition structure formed in the macropore characterizing this invention. 4 is a SEM photograph of a cross section of a ceramic porous body of Comparative Example 1. FIG.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments for carrying out the invention. The following description is for making the gist of the invention better understood and is not intended to limit the present invention. As a result of intensive studies to solve the problems of the prior art described above, the present inventors have made a conventional gelation freezing method for producing a porous body using a ceramic raw material powder and a gelling agent solution. If a special structure is added to the above, it is possible to form a partition structure in which a large number of node-shaped partition walls are formed inside the cylindrical macropores, and the ceramic porous body having such a structure is It was found to be extremely useful as a heat insulating material. More specifically, cylindrical macropores derived from the gelling agent are formed in the freezing step by an extremely simple means of containing an organic compound or an inorganic compound that lowers the freezing point of the gel body in the raw material. When ice crystals are formed with freeze concentration, the freezing point of the gel body is lowered by the added organic or inorganic compound, and the barrier rib structure has a large number of node-like barriers spanned inside the macropores. Was found for the first time, and the present invention was completed based on this finding.

Hereinafter, the present invention will be described with reference to an example of a method for producing a ceramic porous heat insulating material of the present invention. The production method of the present invention includes a gelation step of obtaining a gel body from a material containing a ceramic raw material powder and a gelling agent solution,
Freezing step of freezing the obtained gel body to obtain a frozen body, drying to remove ice from the frozen body obtained in the freezing step to obtain a dried body, and drying to obtain porous ceramics by firing the dried body -It has a baking process. In particular, in the gelation step, in addition to the ceramic raw material powder and the gelling agent solution, an organic compound or an inorganic compound that causes a freezing point depression of the gel body is added to the raw material, and the gel containing these A porous ceramic having a unique partition wall structure is produced inside the macropores by producing a body, and freezing, drying and firing the gel body. Except for the materials used in the gelation step, basically, the technical matters described in JP 2008-201636 A can be used.

In the gelation step, first, the ceramic raw material powder and the gelling agent solution in which the gelling agent is dissolved in water (hereinafter also simply referred to as “gelling agent solution”), together with this, the freezing point lowering of the gel body A mixture containing an organic compound or an inorganic compound (hereinafter, also referred to as “gel body freezing point lowering additive”) and a ceramic raw material powder content of 1 to 50% by volume is prepared. The raw material powder used in the present invention may be a ceramic powder dispersed in water (including carbon powder in the present invention), and has one feature that it is a manufacturing method independent of the raw material. For this reason, there is no restriction | limiting in the kind of raw material, Ceramic raw material powder can be selected suitably in consideration of cost, the intensity | strength of a final product, etc. For example, known ceramic powder particles can be used singly or in combination of two or more. Specifically, alumina, zirconia, silicon carbide, silicon nitride, boron nitride, cordierite, or carbon can be used. A small amount of sintering aid can be added to these.
Prepare a slurry (mixture) containing the raw material powder, water, gelling agent and gel body freezing point depressant additive blended to the above volume%, then pour the prepared slurry into a mold and gel Create a body.

  The production method of the present invention is a ceramic having a high porosity, having a unique shape of a partition structure in which a large number of node-shaped partition walls are formed inside macro pores without depending on the type of starting material. A porous material can be provided. Therefore, although not particularly limited by the shape and size of the raw material powder, the raw material powder can be selected in consideration of the environment and cost to be used. For example, the particle size of the raw material powder is preferably about 0.01 μm to 100 μm when defined as the diameter of the raw material particles. Particularly desirable is a range of 0.01 μm to 5 μm. This is because when the slurry is produced, the raw material powder is crushed and is uniformly dispersed within the slurry. If the particles are larger than this, they will settle and a homogeneous gel body may not be obtained, which is not desirable.

  Further, in order to make the porosity of the porous ceramic characterizing the present invention to be a suitable 50 to 99 volume%, the content of the raw material powder is 50 volume% or less and the water content is 48. 9 vol% or more, the content of the gelling agent is 1 to 5 vol%, and the content of the freezing point lowering additive of the gel body is 0.1 to 13 vol% (0.1 to 15.0 when converted to mass%) Mass%), and further, the freezing point depressing additive of the gel body is preferably 0.1 to 5% by volume. When the content of the gelling agent is 1 to 5% by volume, if it is less than this, gelation does not proceed, and the function as the gelling agent may not be sufficiently exhibited. However, if the amount of the gelling agent is too large, the gel strength is increased and the water separation property during freezing tends to be inferior. As described above, the content of the freezing point depressant additive in the gel body is preferably 0.1 to 5% by volume, and by containing in this range, the formation of a better partition structure can be more stably performed. Can be obtained.

  As the gelling agent used in the gelation step, for example, a gelling water-soluble polymer such as gelatin can be preferably used. Of course, the present invention is not limited to this, and any water-soluble polymer that can be gelled, such as those listed below, can be used. For example, the N-alkylacrylamide polymer, N-isopropylacrylamide polymer, sulfomethylated acrylamide polymer, N-dimethylaminopropylmethacrylamide polymer, poly An alkylacrylamide polymer, alginic acid, polyethyleneimine, starch, carboxymethylcellulose, gelatin, hydroxymethylcellulose, sodium polyacrylate, polyvinyl alcohol, polyethylene glycol, agar, polyethylene oxide, or the like can be used.

  Examples of the freezing point depressant additive of the gel used together with the gelling agent as described above include, for example, acrylamide polymer, alginic acid polymer, polyethyleneimine polymer, methylcellulose polymer, polyacrylic acid polymer, Polycarboxylic acid polymers, polyethylene glycol, polyprene glycol, ethylene glycol, lower alcohols having 1 to 3 carbon atoms, nitrates, chloride salts, and the like can be used. More specifically, polyacrylate, aluminum nitrate · 9 hydrate, and the like can be used. As described above, these compounds are about 0.1 to 15.0% by mass, more preferably 0.1 to 5.0% by mass with respect to the ceramic raw material powder. It is good to contain.

  In the production of the gel body in the present invention, for example, a slurry having the above-described mixing ratio is produced, the slurry is poured into a mold, and solidified in a state where water is held in the gel to be gelled. By this gelation, the ceramic raw material powder is fixed in the gel.

  Next, in the freezing step, the gel body cast into the mold is frozen. For example, a frozen body in which ice crystals are oriented in the gel body can be obtained by cooling from a part or the entire surface of the mold. As a freezing method, a known cooling method such as a normal freezer or a freezing tank may be used.

  The freezing temperature for producing the frozen body is not particularly limited as long as the water retained in the gelling agent is frozen. However, according to the study by the present inventors, in the range of −10 to −20 ° C., the ice crystals are coarsened, and the pore (macropore) inner diameter tends to be larger than about 300 μm and coarse. It is not desirable because it becomes difficult to form a large number of nodular films on the inner wall of the pores at a favorable pitch, and as a result, it becomes difficult to form a desired partition structure. Therefore, the freezing treatment is preferably performed at a temperature lower than −20 ° C., for example, at a temperature of about −40 ° C. so that the macropore inner diameter is about 50 to 200 μm. Although it depends on the inner diameter of the formed macropores, according to the study by the present inventors, in order to make the microstructure more difficult to pass heat and gas and more useful as a heat insulating material, the distance between the membranes is macroscopic. It is preferable that a large number of node-like partition walls are formed at about 10 to 100% with respect to the inner diameter of the pores. More preferably, it is more preferable that a large number of node-like partition walls are densely formed at a pitch of about 10 to 40% with respect to the inner diameter of the macropores.

  Next, in the drying / firing step, the ice is dried and removed from the frozen body obtained as described above, and then fired. During this treatment, it is important to remove only ice so as not to destroy the structure of the raw material powder and ice crystals that are constituents of the frozen body. In other words, it is desirable to adopt an ice removal method that has little dimensional change and less risk of sample destruction. An example of a drying method that is less likely to cause dimensional changes and sample destruction is a freeze drying method, and such a method is suitable as a drying method applied to the present invention. The freeze drying method is a method in which only ice is removed by directly sublimating ice in a frozen body under reduced pressure. This method is suitable as a method for removing ice from the frozen body and drying it in the method of the present invention because the ice is directly sublimated into water vapor from the surface of the frozen molded body, so that the dimensional change is small.

  In the firing step performed after drying, the firing temperature can be appropriately determined in order to ensure the strength of the porous body to be obtained, depending on the type of raw material powder used. For example, when the ceramic raw material powder is silicon carbide or silicon nitride, 1,500 to 2,300 ° C., when alumina is 1,100 to 1,600 ° C., and when zirconia is 1,200 to 1 , 600 ° C., 1,400-2500 ° C. for boron nitride, 1,300-1,500 ° C. for cordierite, 1,000-2,500 ° C. for carbon It is desirable to fire each.

Next, the present invention will be described more specifically based on examples.
<Example 1>
A zirconia powder (manufactured by Tosoh: 8Y) having a specific surface area of 7 m ² / g was used as the ceramic raw material powder. This is a zirconia powder containing 8 mol% yttria. A slurry was prepared by mixing 10% by volume of the zirconia powder, 86% by volume of distilled water, and 1% by volume of polyacrylate as a freezing point depressant additive for the gel body. Further, a gelling agent (gelatin, 3% by volume of Wako Pure Chemical Industries, Ltd.) was added to prepare a slurry. And the obtained slurry was cast to the shaping | molding die, and it gelatinized in the refrigerator. After gelation, the gel body was cooled together with the mold in a freezing tank at −40 ° C. for 1 hour to obtain a frozen body. The obtained frozen body is removed from the mold and dried in a freeze drying apparatus for 12 hours to obtain a dried body. Thereafter, the dried body is fired in a firing furnace at 1,500 ° C. for 2 hours to obtain a porous ceramic body. Obtained. The porous body obtained in this example as described above was evaluated by measuring the porosity, SEM observation of the internal structure, and measuring the air permeability, thermal conductivity, and strength. FIG. 1 is an SEM photograph of a ceramic porous body. As can be seen from the figure, the ceramic macroporous body is spanned upright on the inner wall of the open or closed cylindrical macropores. It has a structure in which a large number of partition walls are formed, as if they were bamboo shoots. The evaluation method and standard of the ceramic porous body will be described later. The obtained evaluation results are summarized in Table 1.

<Example 2>
Silicon nitride powder (manufactured by Ube Industries: SN-COC) having a specific surface area of 10 m ² / g was used as the ceramic raw material powder. This is a silicon nitride powder containing 5% by weight yttria and 2% by weight alumina. 10% by volume of this silicon nitride powder, 87% by volume of distilled water, 1 mass of distilled water containing aluminum nitrate nonahydrate (manufactured by Wako Pure Chemical Industries, Ltd.), which is an inorganic salt, as a freezing point depressant additive for the gel body A slurry was prepared by adding 3% by volume of a gelling agent (gelatin, manufactured by Wako Pure Chemical Industries, Ltd.). And the obtained slurry was cast to the shaping | molding die, and it gelatinized in the refrigerator. After gelation, the gel body was cooled together with the mold in a freezing tank at −60 ° C. for 1 hour to obtain a frozen body. The obtained frozen body was removed from the mold and dried with a freeze drying apparatus for 12 hours to obtain a dried body, and then the dried body was fired in the same manner as in Example 1 to obtain a ceramic porous body. FIG. 2 is an SEM photograph of the obtained porous body. As can be seen from the figure, in addition to the inorganic salt, as in the case where the polyacrylate of Example 1 was used, a cylindrical shape was obtained. A structure in which a large number of partition walls were formed upright on the inner wall of the pores was confirmed. Furthermore, the obtained porous body was evaluated in the same manner as in Example 1, and the evaluation results are shown in Table 1.

<Example 3-1 to Example 3-3>
A zirconia powder (manufactured by Tosoh: 8Y) having a specific surface area of 7 m ² / g was used as the ceramic raw material powder. This is a zirconia powder containing 8 mol% yttria. A slurry was prepared by mixing 10% by volume of the zirconia powder, 86% by volume of distilled water, and 1% by volume of polyacrylate as a freezing point depressant additive for the gel body. Further, a gelling agent (gelatin, 3% by volume of Wako Pure Chemical Industries, Ltd.) was added to prepare a slurry. And the obtained slurry was cast to the shaping | molding die, and it gelatinized in the refrigerator. After gelation, when the gel body is frozen in the freezing tank together with the mold, the freezing temperatures are −10 ° C. (Example 3-1), −30 ° C. (Example 3-2), and −40 ° C. (Example 3- It was adjusted to 3), and each was cooled for 1 hour to obtain frozen bodies. The obtained frozen body is removed from the mold and dried in a freeze drying apparatus for 12 hours to obtain a dried body. Thereafter, the dried body is fired in a firing furnace at 1,500 ° C. for 2 hours to obtain a porous ceramic body. Obtained. Table 2 shows the average pore diameter of the macropores, the presence / absence of the partition structure, and the distance between the films forming the partition structure of the porous body obtained in this example as described above. As can be seen from the table, the higher the freezing temperature, the larger the average pore diameter of the macropores. In Example 3-1, which was frozen at −10 ° C., the average pore diameter was 300 μm, macropores were formed, and the nodular membrane was formed. However, the shape and number were not sufficient, and it was difficult to say that the desired partition wall structure.

<Comparative Example 1>
A porous ceramic body was produced using the same zirconia powder as used in Example 1 by the gelation freezing method using a gelling agent disclosed in JP-A-2008-201636. Specifically, in the method of this comparative example, the same gelling agent as used in Example 1 was used as the raw material, but the polyacrylate used in Example 1 was not included in the raw material. Other manufacturing conditions were the same as in Example 1. The porosity of the obtained porous body, SEM observation of the internal structure, and air permeability were measured and evaluated. FIG. 4 is an SEM photograph of the porous body of the comparative example. As shown in the figure, a large number of communication holes were formed, but no partition wall structure as in the example was found. The evaluation results are shown in Table 1 as in the case of the examples.

<Comparative example 2>
The air permeability, thermal conductivity, and strength of a heat insulating material (Zirker: trade name, manufactured by Zirker Zirconia) manufactured using a commercially available fiber as a raw material were measured. The evaluation results are shown in Table 1 as in the case of the examples.

<Evaluation>
(1) Porosity The porosity was calculated by calculating the density from the size and weight of each ceramic porous body obtained and dividing by the density of the powder. The porosity of the porous body of Example 1, which is an embodiment of the present invention, was as high as 73%. As described in JP-A-2008-201636, the porous material obtained by the gelation freezing method of Comparative Example 1 had a porosity that was almost the same as that of the porous material of Example 1. .

(2) Structure / Structure Each ceramic porous body obtained in Examples 1 and 2 was found for the first time in the present invention within the macropores, as is apparent from FIGS. A partition wall structure was formed. That is, a thin film shape that is formed by walls arranged in the vertical direction in the figure, is upright on the inner wall of the macropores that are in communication or not in communication, and is thinner than the thickness of the inner wall, In this case, a large number of partition walls like a bamboo shoot are formed in the horizontal direction in the figure. On the other hand, as shown in FIG. 4, the porous body of Comparative Example 1 produced by the conventional gelation freezing method has very fine pores as described in JP-A-2008-201636. It was excellent, and formation of a large number of partition walls as in the examples shown in FIGS. 1 and 2 was not recognized.

(3) Air permeability and thermal conductivity The air permeability of the ceramic porous body was measured according to JIS K7126-1. The porous body of Example 1 having a partition wall structure found for the first time in the present invention had an air permeability of 4 × 10 ⁻¹³ m ² , whereas Comparative Example 1 produced by a conventional gelation freezing method. The porous body had an air permeability of 5 × 10 ⁻¹² m ² . Furthermore, it was confirmed that the porous body, which is the product of the present invention, has a very low value of air permeability as compared with conventional heat insulating materials made of various porous bodies. On the other hand, the thermal conductivity was almost the same between the product of the present invention and the comparative product. Furthermore, the strength was 10 MPa in the product of the present invention, whereas the heat insulating material using the fiber of Comparative Example 2 as a raw material showed a strength of 5 MPa, which is 2 MPa. This is because the product of the present invention has a partition structure formed inside the macropores and capable of inhibiting the movement of gas and heat, in addition to being able to achieve a high porosity due to the presence of macropores. It is thought that this is because. The results are shown in Table 1.

(4) Average pore diameter of macropores The average pore diameter of the macropores of the ceramic porous body was measured and calculated from SEM observation results. Specifically, the surface orthogonal to the direction in which the cylindrical macropores are oriented is ground with a surface grinder, the ground surface is observed with SEM, and an arbitrary line is drawn on the obtained SEM photograph, A so-called line intercept method was used in which the part where the line and each pore crossed was the pore diameter. The number of measurements was 500 per sample, and the value corresponding to the cumulative frequency 50 from the frequency distribution of the obtained pore size was defined as the average pore size. In Example 3-1, the average pore diameter was 300 μm, and formation of a partition structure was observed, but a clear node was not formed, which was not desirable. On the other hand, in Examples 3-2 and 3-3, the average pore diameter was smaller than that in Example 3-1, and a partition wall structure having many nodular films at a favorable pitch was confirmed. This is because, in the ceramic porous body of the present invention, when the freezing temperature is as high as −10 ° C. and the macropores become coarse, the node formed like a membrane in the cylindrical macropores maintains the shape of the membrane. This is thought to be because it breaks.

  As described above, the technology of the present invention can be applied to various ceramic raw material powders, and has a high strength ceramic porous body with excellent heat insulation and gas blocking performance. Therefore, the utilization of the present invention is considered to be possible in a wide range, and extremely high applicability in the industry is expected.

Claims (6)

A method for producing a ceramic porous heat insulating material for producing a porous ceramic having a partition structure using a gelation freezing method,
A gel body preparation step for obtaining a gel body from a material containing a ceramic raw material powder and a gelling agent solution, a freezing step for freezing the obtained gel body to obtain a frozen body, and the freezing step A drying / firing step for firing the dried body obtained by removing ice from the frozen body,
In the gel body preparation step, N-alkyl acrylamide polymer, N-isopropyl acrylamide polymer, sulfomethylated acrylamide polymer, N-dimethylaminopropyl methacrylamide polymer, polyalkyl acrylamide polymer, alginic acid A gelling agent solution in which any of the gelling agents of polyethyleneimine, starch, carboxymethylcellulose, gelatin, hydroxymethylcellulose, sodium polyacrylate, polyvinyl alcohol, polyethylene glycol, agar or polyethylene oxide is dissolved in water. Used together with this, an organic compound or an inorganic compound that causes a freezing point depression of the gel body is contained as an additive for lowering the freezing point of the gel body, the content of the ceramic raw material powder is 1 to 50% by volume, and contains water Amount A slurry having a content of 48.9% by volume or more, a gelling agent content of 1-5% by volume, and a gel body freezing point depressing additive content of 0.1-5% by volume was prepared, and then prepared. Pour the slurry into a mold to make a gel body ,
In the freezing step, at the time of freezing, when the ice crystals moisture of the gel material became been cooled Hosoanagen is formed, a tubular macro ice crystals from the gelling agent, the macro ice crystals In the inside, a frozen body having a partition structure is obtained by forming a large number of nodal partitions by freeze concentration and freezing point depression of the gel body,
By removing the ice from the frozen body in the drying and firing step, it is suspended in a cylindrical macropore having an inner diameter of 10 to 300 μm upright on the inner wall of the macropore made of the same material as the macropore. A porous ceramic having a partition wall structure in which a large number of nodular barrier ribs are formed with a plurality of the membranes arranged at a pitch of 10 to 100% of the inner diameter of the macropores. A method for producing a ceramic porous heat insulating material. An acrylamide polymer, alginic acid polymer, polyethyleneimine polymer, methylcellulose polymer, polyacrylic acid polymer, wherein the organic compound or inorganic compound causing the freezing point depression of the gel body is different from the gelling agent. , polycarboxylic acid polymer, polyethylene glycol, polyprene Ropi glycol, ethylene glycol, 1 to 3 carbon atoms a lower alcohol, according to claim 1, wherein at least either selected from the group consisting of nitrates and chlorides salts A method for producing a ceramic porous heat insulating material. The method for producing a ceramic porous heat insulating material according to claim 1 or 2 , wherein the gel body is frozen at -10 ° C or lower in the freezing step . The ceramic according to any one of claims 1 to 3, wherein the ceramic raw material powder has at least one selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, boron nitride, cordierite, and carbon. A method for producing a porous heat insulating material. Freeze the gel body made of ceramic raw material powder, gelling agent solution, and material containing organic compound or inorganic compound that causes freezing point depression of gel body different from gelling agent. , Obtained by gelation freezing method using ice crystals formed at the time of freezing as a pore source, and having a partition structure in which a large number of nodal partitions are formed inside a cylindrical macropore derived from a gelling agent I porous ceramics der,
A large number of membranes having a thickness of 1 to 10 μm, in which the partition wall structure is stretched upright on the inner wall of the macropores, which is made of the same material as the macropores, in a cylindrical macropore having an inner diameter of 10 to 300 μm formed by, insulation distance between the film and the film is characterized in der Rukoto having multiple sections shaped partition arranged at 10-100% of the pitch of the inner diameter of macroporosity. The porosity of the porous ceramics is a 50 to 99% and an air permeability of that ceramics porous heat insulating material according to claim 5 which is ^{1 × 10 -20 ~1 × 10 -12} m 2 .