JPH07138084A - Gradient porosity lightweight ceramics molding and method for manufacturing the same - Google Patents

Abstract

(57) [Summary] [Purpose] The main object of the present invention is to provide a porosity-graded lightweight ceramics molded product having high strength and surface smoothness and capable of exhibiting excellent thermal shock resistance. [Configuration] 1. A molded body composed of oxide-based or non-oxide-based ceramics, wherein (a) the porosity of the entire molded body is 30 to
90%, (b) the dense layer exists over a depth of 5 to 50 μm from the surface, and (c) the porosity continuously increases from the dense layer toward the center of the compact. A characteristic lightweight ceramics compact with a porosity gradient. 2. After adding a foaming liquid having a bubble diameter of 10 to 2000 μm to an oxide-based or non-oxide-based ceramic powder slurry and stirring the slurry, the slurry is cast-molded at a deposition rate of 110 μm / min or less, and then demolded, A method for producing a porosity-graded lightweight ceramics molded body, which comprises degreasing and firing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a porosity-graded lightweight ceramic molding which can be widely used in various industrial fields such as setters and mortars used for firing electronic materials, ceramic materials, powder alloy materials and the like. The present invention relates to a body and a manufacturing method thereof.

[0002]

2. Description of the Related Art The conventional lightweight ceramics molded body made of a porous material has a small specific gravity when it is used as a firing tool material, resulting in a small heat capacity. It requires less energy. Therefore, as compared with the case of using an ordinary ceramic molded body, there are advantages that good thermal efficiency can be obtained and the manufacturing cost can be suppressed.

However, the strength is low because of the porous body,
Moreover, since the pores are exposed on the surface layer, there is a problem that a small object to be fired falls into the exposed pores and the firing becomes insufficient.

Moreover, generally, a lightweight ceramic molded body has a drawback that it is inferior in thermal shock resistance, but this is due to the existence of pores. That is, in the lightweight ceramics molded body made of a porous body, there is a limit to the improvement of thermal shock resistance as long as the pores are present.

[0005]

SUMMARY OF THE INVENTION Accordingly, the main object of the present invention is to provide a porosity-graded lightweight ceramics compact having high strength and surface smoothness and capable of exhibiting excellent thermal shock resistance. To do. A further object of the present invention is to provide a manufacturing method capable of controlling a desired bulk specific gravity and relatively easily obtaining a molded product having the above structure.

[0006]

The inventors of the present invention have conducted extensive studies in view of the above-mentioned problems of the prior art, and as a result, in the case of forming a raw material slurry into which a large amount of foaming liquid has been introduced by cast molding under constant conditions. Found that a molded product having a peculiar structure can be obtained, and further found that this molded product has high strength and surface smoothness and exhibits excellent thermal shock resistance in spite of being porous, The present invention has been completed.

That is, the present invention relates to the following molded body and manufacturing method.

1. A molded body made of oxide-based or non-oxide-based ceramics (a) The porosity of the entire molded body is 3
0 to 90%, and (b) the dense layer is 5 to 50 μm from the surface.
A porosity-graded lightweight ceramics compact which is present over a depth of m and (c) has a porosity that continuously increases from the dense layer toward the center of the compact.

2. A slurry obtained by adding a foaming liquid having a bubble diameter of 10 to 2000 μm to an oxide-based or non-oxide-based ceramics powder slurry and stirring the slurry is a deposition rate 11
After cast molding at 0 μm / min or less, demolding, degreasing,
A method of manufacturing a porosity-graded lightweight ceramics compact characterized by firing.

The molded article of the present invention will be described below.

The porosity-graded lightweight ceramics compact of the present invention is a compact comprising an oxide-based or non-oxide-based ceramic, and the surface layer of which (a) has a porosity of 30 to 90% as a whole. And (b) the dense layer is 5 to 50 from the surface.
It exists over a depth of μm, and (c) has a peculiar structure in which the porosity continuously increases from the dense layer toward the center of the compact.

As the material of the molded body, any kind of ceramics can be used as long as it can be applied to the manufacturing method described below, and virtually any known oxide-based or non-oxide-based ceramics can be used. It can be used as a material for the molded article of the invention. Specifically, for example, oxide-based materials include alumina-based materials, mullite-based materials, and zirconia-based materials. Examples of non-oxide materials include silicon carbide materials, silicon nitride materials, aluminum nitride materials, boron nitride materials, and graphite materials.

The porosity of the whole molded body is usually 30 to 90%.
It is preferably about 50 to 80%. When the porosity is less than 30%, the characteristics as a lightweight body may not be exhibited, which is not preferable. If it exceeds 90%, the strength decreases. The size of the pores depends on the material forming the molded body, but is usually about 20 to 4000 μm.

The dense layer is usually 5 to 5 from the surface of the molded body.
Present over a depth of 0 μm. Here, the dense layer referred to in the present invention means a layer having a porosity of usually about 0 to 5%.
When this dense layer is a layer as thin as less than 5 μm from the surface, both surface smoothness and strength decrease. When high strength is required, the thickness from the surface may exceed 50 μm within a range that does not impair the lightness. Also,
When the wall thickness of the molded body is large, it may exceed 50 μm within a range not exceeding ¼ of the thickness.

The smoothness (R _max ) of the surface of the molded product is
It may be appropriately set according to the amount of organic substances contained in the object to be fired, the firing rate, and the surface accuracy of the object to be fired, usually 3 to 50.
It is about μm. If a precise surface is not required, it is advantageous that the surface roughness is large from the viewpoint of promoting degreasing, so that it may be out of the above range, and if necessary, it may be embossed. .

The molded product of the present invention has a structure in which the porosity continuously increases from the dense layer toward the center of the molded product. The rate of increase in porosity (gradient of porosity) is
Although it varies depending on the manufacturing conditions, the raw materials used, etc., it is not uniform, but for example, as shown in FIG. 1 or 2 below, in porous alumina ceramics, it is relatively high at a certain depth from the surface layer, and then relatively gentle. It is inclined. From the viewpoint of strength, the porosity of the central part of the molded body is preferably 95% at maximum. In the molded product of the present invention having such a peculiar structure, even if cracks occur inside the molded product, the progress of cracks is suppressed because the porosity decreases toward the surface of the molded product, and crack growth occurs. As a result, it exhibits excellent thermal shock resistance.

Since the pores in the molded body have elongated shapes, stress concentration tends to occur more easily as defects.
It is preferably as close to a spherical shape as possible. Further, it may have a structure of continuous pores, independent pores or a mixed type thereof.

Next, the method for producing the molded article of the present invention will be described.

First, a ceramic slurry is prepared. A ceramic powder of the above-mentioned molded body is used as a raw material, water is added thereto, and a slurry is prepared according to a conventional method.
Usually, the amount of water is preferably 20 to 50 parts by weight with respect to 100 parts by weight of the ceramic raw material. If the amount is less than 20 parts by weight, it becomes difficult to adjust the slurry. Again 50
When it exceeds the weight part, it takes a long time to cure after casting. Further, in the present invention, various additives such as known lubricants and dispersants may be added as necessary.

Next, by adding a foaming liquid separately prepared with a foaming agent to the above slurry and stirring, or by directly adding a foaming agent to the above slurry and stirring, air bubbles are generated in the slurry. Introduce.

Here, the foaming liquid referred to in the present invention means a foam-like body composed of bubbles prepared by a known foaming agent and the like, and the foaming agent referred to in the present invention is to be added to and mixed with a ceramic slurry. Those that form bubbles are collectively referred to.
That is, the foaming agent is not particularly limited as long as it can form bubbles, and a foaming agent, a foaming agent, a surfactant and the like are also included in the foaming agent of the present invention. Specifically, as the foaming agent, aluminum fine powder, silicon fine powder,
Examples of the foaming agent include protein-based foaming agents and egg white, and examples of the surfactants include alkylbenzene sulfonates and higher alkyl amino acids. In addition, in the present invention, it is preferable to use a protein-based foaming agent in view of low cost. Further, in the present invention, known thickeners, sizing agents and the like can be appropriately added as necessary. Examples of the thickener, sizing agent and the like include methyl cellulose, polyvinyl alcohol, sucrose, molasses and the like. By adding these, the strength of the bubbles in the slurry can be improved and the bubbles can be stabilized. The foaming liquid may be prepared by a conventional method using the foaming agent or the like.

The slurry in which bubbles are introduced is poured into a mold such as a gypsum mold, and cast molding is performed according to a usual method. In this case, the solid content floating on the bubble surface moves to the surface layer, and the moving speed is 110 at the initial inking speed of the casting mold.
By setting it to be equal to or less than μm / min, preferably equal to or less than 80 μm / min, it is possible to impart and control the porosity inclination characteristic of the molded body. That is, when performing cast molding,
First, bubbles are crushed on the plaster mold surface to form a dense layer,
After that, the inking rate gradually becomes slower due to the formation of the dense layer, and the bubbles remain. After a while, the inking rate is further reduced, the diameter of the bubbles remaining inside the compact is increased, and the amount of bubbles is also increased. As a result, a lightweight ceramic compact whose porosity changes from the surface layer toward the center is obtained. .

When the above-mentioned deposition rate exceeds 120 μm / min, it becomes difficult to impart the graded porosity characteristics.
That is, the distribution of pores becomes uniform, which is not preferable. The lower limit of the inking rate is not particularly limited as long as bubbles can be confined in the molded body, and may be appropriately set depending on the use of the molded body and the like.

In general, the dense layer tends to be thicker when the inking speed is increased. Therefore, for example, when a thick dense layer is required, a dense layer having a thickness of 10 to 100 μm can usually be formed by setting the inking rate to about 80 to 110 μm / min. Furthermore, put the gypsum mold in the decompression device and adjust the water absorption of the gypsum mold while controlling the pressure,
It is also possible to control the dense layer to a desired thickness.

In the present invention, it is possible to control the degree of inclination of the porosity of the molded body by inserting a positive electrode and a negative electrode of a negative electrode into a slurry in which bubbles are introduced and applying a voltage. is there. That is, the solid content floating on the surface of the bubble moves along with the bubble toward the electrode opposite to the particle charging by applying a voltage, but in this case, the moving speed of the solid content is controlled by changing the voltage. The degree of inclination can be changed. The voltage to be applied may normally be a DC voltage of 100 to 200V. 1
If it is less than 00V, the solid content does not sufficiently move, and if it exceeds 200V, the moving speed becomes too fast, which makes it difficult to form a dense layer, which is not preferable. The method of controlling the voltage varies depending on the use of the molded body and the type of material. For example, the voltage of 200 V is first applied to form the dense layer, and the voltage is adjusted after the dense layer has a desired thickness. Can be done by gradually lowering.

Then, the molded product of the present invention is obtained by demolding and degreasing according to a conventional method and then firing. The firing conditions are usually about 1300 to 1700 ° C. and about 1 to 5 hours.

[0027]

According to the manufacturing method of the present invention, since the ceramics slurry containing a large amount of air bubbles is molded by casting while controlling the inking rate, the porosity of the dense layer to the central part of the molded body is increased. It is possible to obtain a ceramic molded body having a peculiar structure in which it continuously increases toward.

Despite being porous, the molded article of the present invention has high strength and surface smoothness, and can exhibit excellent thermal shock resistance. Utilizing its unique structure, it can be widely used in applications such as firing jars, setters, shelves, and heat insulating bricks.

[0029]

EXAMPLES Examples and comparative examples will be shown below to further clarify the characteristics of the present invention.

Example 1 A lightweight ceramic compact was prepared using alumina ceramic powder as a raw material.

First, the alumina-based ceramic powder 300
To 100 g of water, 100 g of water, 1.5 g of a polyacrylic acid ammonium salt-based dispersant and 1.5 g of a paraffin wax-based lubricant were added, and the mixture was stirred with a propeller mixer to prepare a ceramics slurry.

Next, an average of about 150 μm prepared separately using a protein-based foaming agent containing 0.2% saccharose.
300 ml of a foaming liquid consisting of bubbles having a size of m (distribution range of 20 to 230 μm) was added to the above slurry and stirred with a propeller mixer. This foam slurry is applied to the inking speed of 80
It was cast in a gypsum mold of μm / min, demolded after 24 hours, and the bulk specific gravity of the obtained green body was measured. As a result, it was 0.62. Further, it was confirmed by observing the fracture surface of this molded body that a dense layer of 35 μm was introduced into the surface layer and pores of 40 to 1500 μm were introduced therein. The pores were almost spherical and had a mixed type structure of independent pores and continuous pores.

The above-mentioned compact was heated in air at 600 ° C. for 5 hours to be degreased, and then fired at 1500 ° C. for 2 hours to obtain a lightweight ceramic compact of the present invention. At this time, no large warp or crack was observed in the molded body, and it was confirmed by observing the fracture surface of the molded body that the dense layer of 30 μm was introduced in the surface layer and the pores of 30 to 1200 μm were introduced therein. It was Moreover, the result of having investigated the porosity from the surface layer to the central portion of the molded body is shown in FIG. From this, it is understood that the porosity continuously increases from the surface layer portion toward the central portion.

Furthermore, the porosity, strength, and
The spalling resistance and other properties were also measured. The results are shown in Table 1.

Comparative Example 1 After casting using a gypsum mold having a wall thickness of 120 μm / min,
A molded body was produced in the same manner as in Example 1 except that the mold was removed after 16 hours. When the obtained molded product was examined, the bulk specific gravity, the thickness of the dense layer, and the overall porosity were almost the same as those of the molded product of Example 1, but the internal porosity was uniform.
Table 1 shows the results obtained by measuring the strength and spalling resistance of the obtained molded product.

[0036]

[Table 1]

From the results shown in Table 1, it can be seen that the molded product of the present invention in which the porosity is increased in a tilted manner exhibits a particularly excellent effect on thermal shock resistance.

Example 2 An average of about 50 μm (distribution range: 10 to 12) prepared separately with a protein-based foaming agent containing 0.2% of sucrose.
A molding was produced in the same manner as in Example 1 except that 200 ml of a foaming liquid consisting of bubbles having a size of 0 μm) was added and the mold was removed 20 hours after casting.

The results of examining the porosity of the molded body are shown in FIG. 1, and the porosity, strength and spalling resistance of the molded body are shown in Table 2.

Comparative Example 2 After being cast using a gypsum mold with a wall thickness of 120 μm / min,
A molded body was produced in the same manner as in Example 1 except that the mold was removed after 12 hours. When the obtained molded body was examined, the bulk specific gravity, the thickness of the dense layer, and the overall porosity were almost the same as those of the molded body of Example 2, but the internal porosity was uniform.
Table 2 shows the results obtained by measuring the strength and spalling resistance of the obtained molded product.

[0041]

[Table 2]

Example 3 An average of about 200 μm (distribution range 100 to 100 μm) separately prepared by a protein-based foaming agent containing 0.2% saccharose.
400 ml of foaming liquid consisting of bubbles with a size of 300 μm)
Was added, and a molded body was produced in the same manner as in Example 1 except that the mold was removed 32 hours after casting.

The results of examining the porosity of the molded body are shown in FIG. 1, and the porosity, strength, spalling resistance, etc. of the molded body are shown in Table 3.

Comparative Example 3 After being cast using a gypsum mold having a deposition rate of 120 μm / min,
A molded body was produced in the same manner as in Example 3 except that the mold was removed after 25 hours. When the obtained molded product was examined, the bulk specific gravity, the thickness of the dense layer, and the overall porosity were almost the same as those of the molded product of Example 3, but the internal porosity was uniform.
Table 3 shows the results obtained by measuring the strength and spalling resistance of the obtained molded product.

[0045]

[Table 3]

Example 4 A lightweight ceramic compact was produced using silicon nitride ceramic powder as a raw material.

First, silicon nitride ceramic powder 30
100 g of water, 3.5 g of polyacrylic acid ammonium salt-based dispersant and 1.5 g of paraffin wax-based lubricant were added to 0 g, and the mixture was stirred with a propeller mixer to prepare a ceramics slurry.

Next, an average of about 130 μm separately prepared by a resin-based foaming agent containing 0.1% of methyl cellulose.
300 ml of a foaming liquid consisting of bubbles having a size (distribution range of 40 to 250 μm) was added to the above slurry and stirred with a propeller mixer. This foam slurry is applied at a deposition rate of 80 μm
It was cast in a gypsum mold of 1 / min, demolded after 22 hours, and the bulk specific gravity of the obtained molded product was measured and found to be 0.81.
Also, observing the fracture surface of this molded body, 40 μm on the surface layer
It was confirmed that 40 to 1980 μm pores were introduced into the dense layer of FIG. The pores were almost spherical and had a mixed type structure of independent pores and continuous pores.

The above compact was heated in air at 500 ° C. for 10 hours to be degreased, and then fired at 1400 ° C. for 2 hours to obtain a lightweight ceramic compact of the present invention. At this time, no large warp or crack was observed in the molded body, and it was confirmed by observing the fracture surface of the molded body that a dense layer of 35 μm was introduced in the surface layer and pores of 32 to 1800 μm were introduced therein. It was Moreover, the result of having investigated the porosity from the surface layer to the center of the molded body is shown in FIG. From this, it is understood that the porosity continuously increases from the surface layer portion toward the central portion.

Furthermore, the porosity, strength, and
The spalling resistance and other properties were also measured. The results are shown in Table 4.

Comparative Example 4 After pouring using a gypsum mold having a wall thickness of 120 μm / min,
A molded body was produced in the same manner as in Example 4 except that the mold was removed after 15 hours. When the obtained molded product was examined, the bulk specific gravity, the thickness of the dense layer, and the overall porosity were almost the same as those of the molded product of Example 4, but the internal porosity was uniform.
Table 4 shows the results obtained by measuring the strength and spalling resistance of the obtained molded product.

[0052]

[Table 4]

From the results shown in Table 4, it can be seen that the molded product of the present invention in which the porosity increases in a tilted manner exhibits a particularly excellent effect on thermal shock resistance.

Example 5 An average of about 70 μm (distribution range: 30 to 200) prepared separately with a resin-based foaming agent containing 0.1% of methyl cellulose.
A molded product was produced in the same manner as in Example 4 except that 250 ml of a foaming liquid consisting of bubbles having a size of μm) was added and the mold was removed 30 hours after casting.

The results of examining the porosity of the above molded product are shown in FIG. 2, and Table 5 shows the porosity, strength, spalling resistance, etc. of the molded product.

Comparative Example 5 After pouring using a gypsum mold having a deposition rate of 120 μm / min,
A molded product was produced in the same manner as in Example 5 except that the mold was removed after 11 hours. When the obtained molded body was examined, the bulk specific gravity, the thickness of the dense layer, and the overall porosity were almost the same as those of the molded body of Example 5, but the internal porosity was uniform.
Table 5 shows the results obtained by measuring the strength and spalling resistance of the obtained molded product.

[0057]

[Table 5]

Example 6 An average of about 210 μm (distribution range: 10) prepared separately with a protein-based foaming agent containing 0.1% of methylcellulose.
Foaming liquid 400 consisting of bubbles having a size of 0 to 350 μm)
A molded body was produced in the same manner as in Example 4 except that ml was added and demolding was performed 30 hours after casting.

The results of examining the porosity of the molded body are shown in FIG. 2, and Table 6 shows the porosity, strength, spalling resistance and the like of the molded body.

Comparative Example 6 After casting using a gypsum mold having a deposition rate of 120 μm / min,
A molded body was produced in the same manner as in Example 5 except that the mold was removed after 23 hours. When the obtained molded body was examined, the bulk specific gravity, the thickness of the dense layer, and the overall porosity were almost the same as those of the molded body of Example 6, but the internal porosity was uniform.
Table 6 shows the results obtained by measuring the strength and spalling resistance of the obtained molded product.

[0061]

[Table 6]

Example 7 A foam slurry was prepared in the same manner as in Example 1, and a flat plate electrode made of stainless steel was applied to this at an initial voltage of 200 V, and gradually lowered to 100 V in 2 hours to perform electrophoretic casting. Thereafter, demolding, drying, degreasing and baking were performed in the same manner as in Example 1. The change in porosity from the surface layer to the center is shown in FIG. From this, it is understood that the porosity continuously increases from the surface layer portion toward the central portion.

Furthermore, the porosity, strength, and
The spalling resistance and other properties were also measured. The results are shown in Table 7. For reference, the results of Example 1 are also shown.

[0064]

[Table 7]

Example 8 A foam slurry was prepared in the same manner as in Example 4, a flat plate electrode made of stainless steel was applied at an initial voltage of 200 V, and the voltage was gradually lowered to 100 V in 2 hours for electrophoretic casting. Thereafter, demolding, drying, degreasing and baking were performed in the same manner as in Example 4. The change in porosity from the surface layer to the center is shown in FIG. From this, it is understood that the porosity continuously increases from the surface layer portion toward the central portion.

Furthermore, the porosity, strength, and
The spalling resistance and other properties were also measured. The results are shown in Table 8. For reference, the results of Example 4 are also shown.

[0067]

[Table 8]

As described above, the molded product of the present invention has a peculiar structure in which the porosity continuously increases from the surface layer portion toward the central portion, and thus it is possible to exhibit particularly excellent thermal shock resistance. I understand.

[Brief description of drawings]

FIG. 1 is a drawing showing changes in porosity from a surface layer to a central portion of molded articles of the present invention in Examples 1 to 3 and Example 7.

FIG. 2 is a drawing showing changes in porosity from a surface layer to a central portion of molded articles of the present invention in Examples 4 to 6 and Example 8.

Front Page Continuation (72) Inventor Ryoichi Shikata 36-6 Katatazoe, Kawachinagano City, Osaka Prefecture (72) Inventor Shinichi Tanaka 8-11-11 Fukushima, Fukushima-ku, Osaka-shi (72) Inventor Yuzo Kanbara Osaka 2-113, Suwanomorimachi, Hamadera, Sakai-shi 19 (72) Inventor Yasuo Miki 2-12-3406, Nishiki, Kaizuka-shi, Osaka (72) Inventor Yusuke Yamazaki 2-8, Shinborihigashi, Wakayama, Wakayama Prefecture 6

Claims (4)

[Claims] 1. A molded body comprising oxide-based or non-oxide-based ceramics, wherein (a) the porosity of the entire molded body is 30 to 90%, and (b) the dense layer is 5 to 5% from the surface. A porosity-graded lightweight ceramics compact which is present over a depth of 50 μm, and (c) has a porosity that continuously increases from the dense layer toward the center of the compact. 2. A slurry obtained by adding a foaming liquid having a bubble diameter of 10 to 2000 μm to an oxide-based or non-oxide-based ceramic powder slurry and stirring the slurry to obtain a deposition rate of 110 μm.
A method for producing a porosity-graded lightweight ceramics molded product, which comprises cast-molding at m / min or less, and then demolding, degreasing, and firing. 3. The method according to claim 2, wherein the casting rate is 80 μm / min or less. 4. The manufacturing method according to claim 2, wherein the degree of porosity inclination of the obtained molded body is controlled by casting the slurry while applying a voltage to the slurry.