KR20010056771A - The preparation of porous ceramics by using foaming process - Google Patents

Abstract

PURPOSE: Provided is a production process of porous ceramics which utilizes a foam method to form a pore by keeping viscosity to a certain degree and stirring and raises the stability of slurry foam so that it keeps the size of the pore uniform. CONSTITUTION: The production process of porous ceramics by the foam method comprises the steps of: (i) adding 20-35wt% of distilled water and 3-8wt% of viscosity adjuster to 100wt% of inorganic powder; (ii) crushing in a ball-mill to produce slurry with less than 5 micrometer in average granularity and 80-2000cp in viscosity; (iii) putting slurry into a stirrer and adding 0.15-1.50wt% of foaming agent to stir at high rate to form slurry foam; (iv) adding 1-3wt% of gelling agent, stirring at low rate, molding in a certain type and charging into a furnace; and (v) raising temperature to 1100-1600deg.C at 1-3 deg.C/min to fire.

Description

The preparation of porous ceramics by using foaming process

The present invention relates to a method for producing porous ceramics, and more particularly, to form porous ceramics by molding and firing foams formed by foaming ceramic slurry to prepare porous ceramics having high porosity, as well as controlling pore size. The present invention relates to a method for producing porous ceramics by a foaming method.

In general, the porous ceramics form a plurality of pores therein, and the mechanical and thermal properties of the manufactured porous ceramics are determined by the size, shape, porosity, and the continuity of the pores present in the porous ceramics. do.

In particular, porous ceramics are used as lightweight building materials within a specific range due to their low specific gravity and light weight due to the large number of pores artificially formed inside, and also various filters, plastic tools, deodorants, insulation materials, sound insulation materials, fillers, impregnants and fires. The usage is increasing greatly due to various uses such as analysis.

Recently, as the value of use of the microorganisms is attached to the porous ceramics and used as a carrier for wastewater treatment and odor removal, the development of the porous ceramics and the research thereof are being actively conducted.

Representative methods of manufacturing the porous ceramics include a sponge method (polymeric sponge method), a filling method (stacking method) and the bubble generation method (bubble generation method).

The sponge method is a method of using the space occupied by organic matter as pores by mixing the flammable polymer with a ceramic slurry to degrease and calcining. The filling method uses a gap between filler particles by mixing fibrous or granular raw material particles as pores. Way.

In connection with the above-mentioned porous ceramics, Japanese Patent Publication No. 62-25620 discloses a porous aggregate produced by mixing additives with water as a main raw material of a fly ash generated from coal dust or a boiler. Korean Patent Publication No. 62-24370 discloses a method for producing artificial light aggregates foamed using coal ash or shale powder as raw materials, and Japanese Patent Publication No. 62-12186 discloses fine minerals such as rhyolite or crushed stone. To this end, a method for producing an ultra-light aggregate aggregated by adding a foaming agent and a pressure-sensitive adhesive thereto and firing at high temperature is disclosed.

However, the above-mentioned manufacturing method is to form pores by mixing the organic material with the ceramic slurry to form pores and then firing process, because the formed pores are very large compared to the skeletal part, the use of the product is limited and organic matter burning during firing There is a problem that toxic gas is generated according to.

Another method for producing porous ceramics is the bubble generation method, which is a method of preparing a porous ceramic by adding a foaming material that reacts with a raw material mixture to generate a gas.

However, the method by the bubble generation method is difficult to control the porosity and pore size, and also needs to be cured in a reactor such as an autoclave, so a problem arises that raw materials that can be used as starting materials are limited.

Accordingly, the present invention is to solve the above-mentioned problems, it is possible not only to form pores without using a sponge or filler, but also to adjust the porosity and pore size, and by the foam method not limited to the type of starting material. Its purpose is to provide a method for producing porous ceramics.

In order to achieve the above object, the present invention is added to 20 parts by weight to 35 parts by weight of distilled water and 3 parts by weight to 8 parts by weight of the viscosity modifier with respect to 100 parts by weight of the inorganic powder used as ceramics and then pulverized with a ball mill to After preparing a slurry having an average particle size of 5 μm or less and a viscosity of 80 cps to 2000 cps, the slurry was placed in a stirrer and 0.15 parts by weight to 1.50 parts by weight of a foaming agent was stirred at a high speed to form a foam of the slurry, and the gelling agent was 1 A foaming method by adding 3 parts by weight to 3 parts by weight, stirring and mixing again at a low speed, molding and drying in a constant shape, loading it into a furnace, and raising the temperature to 1100 ° C. to 1600 ° C. at a rate of 1 ° C./min to 3 ° C./min. It can achieve by providing the manufacturing method of porous ceramics by this.

20 parts by weight to 40 parts by weight of distilled water and 3 parts by weight to 8 parts by weight of the viscosity modifier are mixed with 100 parts by weight of the inorganic powder used as the ceramic, and then the mixture is ball milled or stirred with an average particle size of 5 μm. The slurry is pulverized to produce a slurry having a viscosity of 80 cps to 2000 cps.

At this time, when the ceramic raw material to be used is not a powder but a bulk, it is preferable to grind the bulk raw material in advance in order to facilitate grinding, and as a usable ceramic raw material, silica including wastes such as fly ash or waste slime can be used. (SiO ₂ ), clay material, zirconia (ZrO ₂ ), alumina (Al ₂ O ₃ ), mullite (mullite: 3Al ₂ O ₃ · 2SiO ₂ ), silicon carbide (SiC), cordierite (Mg ₂ Al ₃ ( Inorganic raw materials that can be calcined and solidified, such as AlSi ₅ ) O ₁₈ ), carbon, and cement, may be used, and two or more ceramic raw materials may be mixed and used.

Distilled water is added not only to maintain the distance between the ceramic raw material particles to enable the dispersion of the slurry, but also to generate bubbles. If the amount is less than 25 parts by weight, the viscosity of the slurry is too high, There is a problem in that the fluidity is lowered and bubbles are not properly formed by stirring, and when the content exceeds 35 parts by weight, the viscosity is low, so that the flowability of the slurry is good. It is preferable to add 25 parts by weight to 35 parts by weight of distilled water since the problem occurs that the foam is easily broken and the foam is not properly formed.

In addition, the viscosity modifier is added to not only facilitate the mixing of distilled water and inorganic raw materials, but also to maintain a constant viscosity so that sufficient strength can be seen when the foam of the slurry is gelled. If the amount is less than 3 parts by weight, the strength of the molded body is lowered, which lowers the workability and also makes it difficult to mix the inorganic raw material with the distilled water. There is a problem that the amount of the viscosity modifier is added in excess of 8 parts by weight. In this case, the mixing of the inorganic raw material and the distilled water is easy, but the gelling time is shortened and the workability is reduced, so that molding is difficult. Therefore, the amount of the viscosity modifier is preferably added in an amount of 3 parts by weight to 8 parts by weight.

In this case, as the viscosity regulator, sodium hexametaphosphate, sodium polyacrylate, sodium polyacrylate, ammonium polyacrylate, polyethyleneimine, and the like may be added.

After adding water and a viscosity modifier to the ceramic raw material, it is pulverized so that the average particle size is 5 μm or less in a ball mill, together with the medium grinding material. When the average particle size exceeds 5 μm, it takes a long time to bake. It is preferable to grind to 5 micrometers or less.

At this time, the formation of foam is greatly influenced by the viscosity of the slurry prepared by grinding, but if the viscosity is less than 80cp, there is a problem that the foaming is not properly formed due to the low viscosity of the foam generated in the foaming process, 2000cp If it exceeds the viscosity is too high agitation is not properly made in the foaming process, it is difficult to form a foam, so it is preferable to adjust the viscosity to 80cp to 2000cp.

The slurry prepared as described above was added to a stirrer, and 0.15 parts by weight to 1.50 parts by weight of a foaming agent was added thereto, followed by stirring at high speed to form a foam of the slurry. Then, 1 part by weight to 3 parts by weight of a gelling agent was added to the slurry foam again. Stirring and mixing at low speed.

In this case, the foaming agent is added to control the pore size and the foaming rate of the porous body. When the foaming agent is added below 0.15 parts by weight, the foam volume can be formed up to twice the initial volume, but it is difficult to form more than that. In addition, there is a problem that the foaming process takes a long time due to the low rate of foam formation, and if the amount exceeds 1.50 parts by weight, the foam volume can be formed up to 5 times and the foam forming time is shortened. It is preferable to add 0.15 parts by weight to 1.50 parts by weight of the foaming agent because a problem occurs that the manufacturing cost increases and the fluidity of the slurry foam increases.

In the above foaming agent, anionic surfactants and cationic surfactants having 10 to 17 carbon atoms in hydrophobic groups are used, and usable cationic surfactants are benzethonium chloride and stearyl trimethyl ammonium chloride. Cetyl trimethyl ammonium chloride and distearyl trimethyl ammonium chloride, and anionic surfactants include triethanloamine salt of lauoyl sarcosine, Sodium lauryl sulfate, ammonium lauryl sulfate, triethanolamine salt of lauryl sulfate polymethacrylate and sodium dodecylbenzene sulfonate sulfonate) There is.

Since the size of the bubble and the stability of the slurry foam is different depending on the type of the surfactant used as the foaming agent, the pore size of the final product can be adjusted by changing the type of surfactant.

After adding the foaming agent together with the slurry and performing high speed agitation at more than 1200rpm in the stirrer, the foam of the slurry is formed, and the stirring is stopped when the volume of the slurry foam is formed to the desired constant height as compared with the volume before the stirring. The volume of the slurry foam is determined according to the stirring time as described above, so that the porosity can be adjusted to control the porosity of the product to be manufactured.

In the above, a stirrer for generating bubbles at a high speed stirring was used a general domestic or industrial stirrer, the number of rotary blades of the stirrer can be appropriately adjusted in consideration of the size of the stirrer and the volume of the slurry to be formed.

As described above, high-speed agitation has the advantage that pore formation is possible without using a method of forming pores by adding a conventional sponge or flammable additive and firing.

In addition, in the present invention, since the pores are formed before firing, the pore size can be increased as well as the pore size can be adjusted by adjusting the volume of the slurry foam during stirring.

The gelling agent is added to the foam formed in a constant volume as described above, wherein the gelling agent serves to maintain the form of the foam formed by gelling the slurry by reacting with the viscosity control agent.

In particular, when the amount of the gelling agent added is less than 1.0 part by weight, too much time is required for the gel molding, and the strength of the molded body is lowered. When the amount of the gelling agent is added more than 3.0 parts by weight, the gelling time is too fast, and molding is impossible. It is preferable that the addition amount of the gelling agent is added in an amount of 1.0 parts by weight to 3.0 parts by weight, and in the present invention, a water-soluble epoxy resin is used as the gelling agent so that the foam generated when the gelling agent is added is not destroyed.

The mixture to which the gelling agent is added is stirred at low speed so that the gelling agent is evenly mixed so that the slurry can be gelled. At this time, the slow stirring is stirred at a speed of 600 rpm.

The slurry foam to which the gelling agent is added is molded in a predetermined form, dried sufficiently, and calcined by heating up to 1100 ° C to 1600 ° C at a rate of 1 ° C / min to 3 ° C / min.

At this time, if the temperature rises rapidly during the sintering process, internal bubbles expand rapidly and cracks occur. Therefore, the temperature increase rate is preferably 1 ° C./min to 3 ° C./min. The final firing temperature is appropriately determined according to the raw materials of ceramics. It is preferable to bake by adjusting.

Hereinafter, the present invention will be described in detail with reference to the following examples and comparative examples, but the present invention is not limited to the following description.

<Example 1>

After mixing polyethyleneimine with distilled water and a viscosity modifier with respect to 100 parts by weight of the ceramic raw material mullite in parts by weight shown in Table 1 below, and then grinding the raw material particles in a stirring mill as shown in Table 1 below to prepare a slurry, The slurry was added to a stirrer and sodium lauryl sulfate was added as a foaming agent in parts by weight shown in Table 1, and then stirred at a high speed at 1200 rpm to form a slurry of slurry. After addition and low speed agitation and mixing again at 600rpm, injection molding was carried out using a disk mold, and after about 1 hour, the mold was removed, dried naturally, and then heated at a speed of 2 ° C./min for 360 minutes at 1450 ° C. Firing to prepare a porous ceramic, the average pore size and pore by the method described below using the prepared porous ceramic By measuring the variation group, porosity and flexural strength are shown in Table 1 below.

Average pore size and pore size deviation

An image analysis system was used to measure the pore size distribution roll of porous ceramics with foam pore structure. The image analysis system uses a zoom camera or an electron microscope to measure the size of pores using the surface photograph of the porous ceramics. After obtaining surface photographs, the average size and the deviation were calculated by measuring about 1000 pore sizes for each sample using an image analysis system.

-Porosity-

Porosity was calculated by Equation 1 below after measuring the bulk density of the porous ceramics and the density of the raw material particles.

Ε is the porosity, ρ _bulk is the bulk density of the porous ceramics, ρ _particle means the density of the raw material particles.

-Bending strength-

The bending strength is made of a 40mm × 10mm × 10mm rectangular parallelepiped specimen, and the load at the time of failure is measured according to the three-point bending strength measurement method in which a specimen is placed on two parallel supports and a load is applied to the center. After the bending strength was calculated by, the same process was repeated five times to obtain the average value as the bending strength.

Where P is the load at break, L is the distance between the two supports, b is the length of the specimen, and h is the thickness of the specimen.

<Example 2>

A porous ceramic was prepared in the same manner as in Example 1, except that benzethonium chloride was added as a foaming agent in the ratio shown in Table 1 below, and then, in the same manner as in Example 1, using the prepared porous ceramic. Mean pore size and pore size deviation, porosity and bending strength were measured and shown in Table 1 below.

Comparative Example 1

40 parts by weight of distilled water and 0.8 parts by weight of a viscosity modifier were added to 100 parts by weight of cordierite, which is a ceramic raw material, and the raw material particles were pulverized to 2.9 µm in a stirring mill. After heating up at a rate of ℃ / min and baked for 360 minutes at 1300 ℃ to prepare a porous ceramic, using the prepared porous ceramic in the same manner as in Example 1, the average pore size and pore size deviation, porosity and bending strength Was measured and shown in Table 1 below.

Comparative Example 2

10 parts by weight of clay particles were added and mixed uniformly with respect to 100 parts by weight of mullite, which is a ceramic raw material, and then compression-molded into a disc shape, heated at a rate of 2 ° C./min, and baked at 1500 ° C. for 180 minutes to prepare a porous ceramic. Next, the average pore size and pore size deviation, porosity and bending strength were measured in the same manner as in Example 1 using the prepared porous ceramics, and are shown in Table 1 below.

division water Viscosity Modifier Foam Average pore size (㎛) Pore size deviation (㎛) Porosity (%) Bending strength (MPa) Example 1 15 4.7 0.31 61 52.3 62 56.2 20 4.7 0.31 70 40.3 74 29.4 30 4.7 0.31 98 34.7 81 14.9 35 4.7 0.31 130 35.2 82 13.3 40 4.7 0.31 203 45.7 80 13.2 30 2.0 0.31 72 42.8 70 39.2 30 5.0 0.31 99 35.1 81 14.2 30 9.0 0.31 111 41.7 79 13.1 30 4.7 0.10 73 39.7 71 26.5 30 4.7 0.50 98 32.9 82 12.5 30 4.7 1.67 125 37.4 79 11.6 Example 2 15 4.7 0.31 124 45.2 63 50.8 30 4.7 0.31 201 65.2 82 11.2 40 4.7 0.31 310 73.5 80 10.5 30 2.0 0.31 117 77.3 72 27.9 30 5.0 0.31 200 69.4 81 13.6 30 9.0 0.31 196 73.5 79 12.4 30 4.7 0.10 148 78.0 77 25.9 30 4.7 0.48 209 68.4 83 11.6 30 4.7 1.67 211 71.9 80 10.8 Comparative Example 1 - - 85 5.30 Comparative Example 2 80 70.3 40 20.1

As shown in Table 1, in Example 1 using sodium lauryl sulfate as the foaming agent, the addition amount of the viscosity modifier is changed to 15 to 40 parts by weight in a fixed state of 4.7 parts by weight, the addition amount of the foaming agent to 0.31 parts by weight In case of adding 15 parts by weight of less than 20 parts by weight of water, the average pore size is 61 μm and 20 parts by weight, the average pore size is 70 μm, and the pore size is 85 μm, and the amount of water is 35 parts by weight. When the excess 40 parts by weight, the pore size is shown to be 203㎛ it can be seen that the average pore size increases as the amount of water added.

However, the pore size deviation measured to determine the uniformity of the pore size is 52.3 μm when 15 parts by weight of less than 20 parts by weight of water is added, 40.3 μm when 20 parts by weight, 34.7 μm when 30 parts by weight, and amount of water added 35 When the amount exceeds 40 parts by weight, the pore size deviation may be 45.7 μm, indicating that the pore size deviation is the smallest when the added amount is within the range of the present invention.

In addition, the porosity tends to increase as the amount of water is generally increased, and appears to be 62% when the amount of water added is less than 20 parts by weight, but the porosity is significantly increased when it is 20 parts by weight or more including the scope of the present invention. In particular, when the amount of water added is 30 parts by weight, it can be confirmed that the porosity can be obtained with a porosity of 81%.

The bending strength tends to decrease as the amount of water added increases, but considering the average pore size, pore size deviation, and porosity, it can be confirmed from Table 1 that the amount of water added is preferably 20 to 35 parts by weight. .

Similarly, in Example 1, when the addition amount of the viscosity modifier was changed while the addition amount of water was fixed at 30 parts by weight and the addition amount of the foaming agent was 0.31 part by weight, the average pore size was 72 when the addition amount of the viscosity modifier was added at less than 3 parts by weight. Μm, pore size deviation was 42.8㎛, porosity was 70%, and when 9 parts by weight exceeding 8 parts by weight was added, average pore size was 111㎛, pore size deviation was 41.7㎛, and porosity was 79%. However, when 5 parts by weight is added within the range according to the present invention, the average pore size is 99 μm, the pore size deviation is 35.1 μm, and the porosity is 81%, indicating that the pore size is uniform and the porosity is also high.

In addition, in Example 1, when the addition amount of the foaming agent was changed while the addition amount of water was fixed to 30 parts by weight and the addition amount of the viscosity modifier to 4.7 parts by weight, the average pore size was 73 when 0.10 parts by weight of the addition amount of the foaming agent was added. Μm, pore size deviation was 39.7㎛, and porosity was 71%. Also, when 1.67 parts by weight exceeding 1.5 parts by weight, average pore size was 125㎛, pore size deviation was 37.4㎛, and porosity was 79%. However, when 0.5 parts by weight of the present invention is added, the average pore size is 98 μm, the pore size deviation is 32.9 μm, and the porosity is 82%, indicating that the pore size is relatively uniform, and the porosity is high. You can see that.

When the addition amount of water is 30 parts by weight, the addition amount of the viscosity modifier 4.7 parts by weight, the addition amount of the foaming agent is 0.31 parts by weight, the average pore size is 98㎛, pore size deviation is 34.7㎛, porosity is 81% appeared in Comparative Example 2 Compared to the average pore size of 80㎛, pore size deviation of 70.3㎛, and porosity of 40%, the average pore size is large and the pore size deviation is very small, so that the pore size is uniform and the porosity is also very high.

In Comparative Example 1, all the large pores of several mm or more exist in the connected through state, so that the average pore size and pore size deviation could not be measured.

In the case of Example 2 using benzene tonium chloride as a foaming agent, it can be confirmed from Table 1 that results similar to Example 1 using sodium lauryl sulfate as the foaming agent, in particular, compared to Example 1 as a whole, the average pore size Is increased greatly and the pore size deviation is increased.

Comparing Example 1 and Example 2, when the foaming agent is appropriately substituted, the pore size can be controlled, and the porosity and the pore size indicate that the porous ceramics can be made relatively uniform.

As described above, the present invention can form pores by stirring and maintaining a constant viscosity without using flammable organic substances or fillers, and also increases the stability of slurry bubbles, so that bubbles formed are stable and the pore size is uniform. In addition, it is a useful invention to provide a method for producing porous ceramics by a foam method to facilitate pore size control and increase porosity.

Claims (6)

20 parts by weight to 35 parts by weight of distilled water and 3 parts by weight to 8 parts by weight of the viscosity modifier are added to 100 parts by weight of the inorganic powder used as the ceramic, and then pulverized with a ball mill to obtain an average particle size of 5 µm or less and a viscosity of 80 cps. A slurry of 2000 cps was prepared, and the slurry was placed in a stirrer, and 0.15 parts by weight to 1.50 parts by weight of a foaming agent was added and stirred at a high speed to form a foam of the slurry, and 1 part by weight to 3 parts by weight of a gelling agent was added again at a low speed. A method of producing porous ceramics by the foam method, characterized in that the stirring and mixing, molding and drying in a constant shape, charged into a furnace and heating to 1100 ° C to 1600 ° C at a rate of 1 ° C / min to 3 ° C / min. The foam according to claim 1, wherein sodium hexametaphosphate, sodium polyacrylate, ammonium polyacrylate, polyethyleneimine, or the like is added as a viscosity modifier. Method for producing porous ceramics by the method. The method for producing porous ceramics according to the foam method according to claim 1 or 2, wherein an anionic surfactant having a carbon number of 10 to 17 and a cationic surfactant is added as a foaming agent. 4. The cationic surfactants of claim 3 include benzethonium chloride, stearyl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride and distearyl trimethyl ammonium chloride. trimethyl ammonium chloride or the like, or as anionic surfactant, triethanloamine salt of lauoyl sarcosine, sodium lauryl sulfate, ammonium lauryl sulfate, triethanol A method for producing porous ceramics by the foam method, comprising adding amine salt lauryl sulfate polymethacrylate, sodium dodedylbenzene sulfonate, and the like. The method for producing porous ceramics by the foaming method according to claim 1 or 2, wherein a water-soluble epoxy resin is added as a gelling agent. The method for producing porous ceramics by the foaming method according to claim 4, wherein a water-soluble epoxy resin is added as a gelling agent.