KR100530093B1 - Method for manufacturing a ceramic body having continuous pore - Google Patents

Abstract

Disclosed is a method of preparing a porous ceramic formed body using a magnetic gelation method and freeze-driing it to produce a ceramic porous body having continuous pores. 250-550 parts by weight of the first powder of the solid waste having non-plasticity and 100-250 parts by weight of the second powder having the plasticity are mixed to form a mixture, and then 200-400 parts by weight of water is added to the mixture to form a slurry. 1-30 parts by weight of the peptizing agent is added to the slurry to form a dispersed slurry, and then 5-15 parts by weight of the flocculant is added to the dispersed slurry to form an aggregate. A molded article is formed by self-gelling of the aggregate, the molded article is dried using a freeze drying method, and then the molded article is sintered to form a sintered article. It is possible to manufacture a ceramic porous body including continuous uniform pores that can be utilized as a ceramic filter or ceramic carrier, and to control the microstructure of the slurry to easily control the characteristics and the size of the pores or the sintered body manufactured from the slurry. have.

Description

Method for manufacturing a ceramic porous body having continuous pores {Method for manufacturing a ceramic body having continuous pore}

The present invention relates to a method for producing a ceramic porous body having continuous pores. More specifically, the present invention relates to a combination of solid wastes composed of plastic and non-plastic powders, and has a gel structure by magnetic gelation by adding an appropriate inorganic flocculant and a peptizing agent. The present invention relates to a method for producing a ceramic porous body which can uniformly form continuous pores in the interior of a sintered body by preparing a molded body and then freeze-drying it to maintain the pore structure of the molded body even after drying.

Generally, as a method of molding a ceramic product, methods such as injection molding, tape casting, and plastic extrusion are known. In conventional molding methods of ceramic products, organic solvents have been used to facilitate the shaping and manipulation of the fine powder dispersed with the organic binder and the plasticizer. Accordingly, a separate organic solvent removal process is required, and during such organic solvent removal process, there is a high possibility that the ceramic product may contract and warp unlike a desired shape. In addition, the mechanical properties of the ceramic product may be degraded due to impurities remaining even after performing the organic solvent removal process. Therefore, considering the environmental impact and economic aspects of the ceramic product manufacturing process based on the characteristics of the ceramic product, a new molding method without using an organic solvent or a polymer additive is required.

Generally, the powder processing of the ceramic compacts comprises the steps of preparing the powder, preparing the powder (slurry) for molding, shaping and drying to the required shape and removing pores, densifying and optimizing for optimum properties. Enhancing the microstructure, and the like.

In each step of the powder process described above, the non-uniformity of the ceramic formed body may be due to the production of the powder itself and the powder (slurry) or may occur in the densification and filling step. In addition, coagulants comprising organic and inorganic substances act as major heterogeneous to the powder. Stress is concentrated in each heterogeneous material, so that a potential flow occurs, which acts as a cause of premature cracking, which in turn causes insulation and mechanical defects.

In order to improve the method of ceramic products, the behavior depends on the interaction between the particles, so it is important to understand the structure of the slip due to the interaction between the particles in the slurry, so it is suspended in the liquid medium. Consideration should be given to the interaction characteristics between the ceramic powder particles present.

Young et al. [J. Am. Ceram. Soc. 74 (3) 612p to 618p (1991)], through a study on the gel-casting method of alumina (Al ₂ O ₃ ) powder to disperse the slurry using a polymer dispersant, To form a macromolecule of macromolecules and to increase the temperature of the slurry to gel by polymerizing.

Graule et al. [Ceramic Transaction, Vol 51, 457p-467p (1994), proposed a direct coagulation casting (DCC) method of agglomeration by reducing the thickness of an electric double layer. However, the method has a problem in that the amount of organic salts to be added is large, and the temperature of the slurry must be adjusted since the aggregation rate varies depending on the temperature of the slurry, and an idle time is required.

According to U. S. Patent No. 5,188, 780 to Lange et al., The pH of the suspension is adjusted to disperse, aggregate and redisperse, which is then molded by pressure filtration and centrifugation to produce a ceramic molded body. The method is advantageous for the molding of the structural material because it has a nearly constant microstructure of the molded article regardless of the content of the solid. However, according to the above method, a compact molded article can be obtained, but it is not suitable for producing a porous molded article, and the process up to producing the molded article has a complicated disadvantage.

As a result, none of the new molding methods described above solves the problem of using an organic solvent.

Serious problems may also arise in the drying process to remove moisture from the ceramic compacts. In the drying process, the capillary force acts between the ceramic particles to cause dry shrinkage. The drying rate is different due to local liquid content differences or partial thickness differences of the product and consequently tends to crack or twist during the drying process.

In order to minimize the problem, the evaporation rate can be slowed down by drying very slowly for a period of time while keeping the relative humidity of the drying chamber constant. In the drying process, moisture migrates from the inside to the surface. As the drying proceeds, the temperature of the molded body can be gradually increased while the humidity is lowered, so that the evaporation rate and the moving speed are properly maintained. Alternatively, the part can be placed on a special support during the drying process to minimize torsion.

However, control of relative humidity and prolongation of the drying time do not always prevent shrinkage or warpage, in particular during the drying process the porosity of the shaped body is reduced and the pore structure is also destroyed.

An object of the present invention is to prepare a molded body by dispersing and agglomerating slurry and self-gellation by poly-silicon hydroxo precipitates (PSHP) using an inorganic dispersant and a flocculant, thereby providing a ceramic porous body having continuous pores. It is to provide a method for producing.

Another object of the present invention is to provide a method for producing a ceramic porous body having continuous pores by freeze drying a ceramic molded body having a uniform pore structure by gelling molding to maintain the porosity and pore structure of the molded body.

It is still another object of the present invention to provide a method for producing a ceramic porous body capable of minimizing disproportionation and uncontrolled phase distribution in the ceramic porous body.

In order to achieve the above objects of the present invention, according to the method for producing a ceramic porous body having continuous pores according to the present invention, about 250 to 550 parts by weight of the first powder of the solid waste having non-plasticity and the second having plasticity About 100 to 250 parts by weight of powder are mixed to form a mixture, and then about 200 to 400 parts by weight of water is added to the mixture to form a slurry. About 1-30 parts by weight of the peptizing agent is added to the slurry to form a dispersed slurry, and then about 5-15 parts by weight of a flocculant is added to the dispersed slurry to form an aggregate. Subsequently, a molded body is formed by magnetic gelation of the aggregate, the molded body is dried using a freeze drying method, and the molded body is sintered to prepare a sintered body. In this case, the molded body is prepared by naturally drying the molded body for about 10 to 15 hours, and then freeze drying for about 30 to 65 hours at a temperature of about -25 to -15 ° C in a freeze dryer. In addition, the solid waste may include at least one or more of coal ash, lime or incineration ash, and the second powder may include one or more of clay, kaolin, pottery or mica minerals, and the peptizing agent may be Na ₂ SiO ₃ , Na _4. At least one of P ₂ O ₇ or Na ₂ CO ₃ , wherein the flocculant comprises waste gypsum containing CaSO ₄ .

According to the present invention, it is possible to manufacture a ceramic porous body including a plurality of pores continuously and uniformly, such a ceramic porous body can be utilized as a ceramic filter or ceramic carrier. In addition, it is possible to easily control the size of the molded body or pores produced from the slurry by adjusting the fine structure of the slurry, and it is possible to easily control the properties of the sintered body because the pore structure of the molded body can be maintained as it is through freeze-drying. Furthermore, since the ceramic porous body is manufactured by inducing peptizing and coagulation of the slurry using a peptizing agent and a coagulant made of inorganic material, not an organic additive as in the conventional case, a separate organic matter removing process is not required, and the process is simplified and Economics can be achieved and eco-friendly ceramic products can be produced. In particular, according to the present invention, since waste gypsum generated in a desulfurization process, phosphoric acid, hydrofluoric acid, boron, or titanium manufacturing process can be recycled as a coagulant to produce a ceramic product, it contributes to environmental problems and at the same time reduces the manufacturing cost of the ceramic product. Can be significantly lowered.

In the present invention, by adsorbing a peptizer on the surface of the highly charged ceramic particles in the aqueous medium, the surface energy of the ceramic particles is lowered to evenly disperse the ceramic particles in the aqueous medium. To this, a flocculant is added to form ceramic particles in the dispersed slurry into small aggregates, and the gelation of these aggregates is used to form a porous new network structure. Thus, when molding the substrate into the desired shape, no additional molding process is required. In the new mesh structure, no sedimentation of particles in the slurry, which was observed in the aggregated structure previously, occurred. Therefore, a complicated shape can be produced relatively easily.

In general, the weak attraction between ceramic particles is generated by the combination of van der Waals attraction and electrostatic repulsion at a certain distance by DLVO theory with a very short range of hydration repulsion of about 5 nm or less. do. In this short range, hydration repulsion blocks the attraction of particles. Thus, under moderate conditions, this force has a higher packing density when the particles are easily slipped and solidified into other particles, when the dried powder or particles form a mesh in contact. Hydration repulsion is a repulsive force acting only when the distance between the particle surfaces is very short (about 5 nm or less), in which case van der Waals attraction becomes increasingly strong (see Ceramic Transaction, Vol. 22, 185p to 201p (1991)). .

According to the present invention, in order to manufacture a ceramic porous body, a second plastic having a plasticity made of clay, kaolin, stone or mica minerals in the first powder having a non-plasticity made of solid waste such as fly ash, stone powder or incineration ash The slurry which mixed powder suitably is used.

Since the coal ash and clay particles of the first and second powders have a hydrophobic surface, the particles are initially strongly coagulated in the slurry according to the DLVO theory, and a mesh is formed between the coagulated particles, causing the particles to settle. When a peptizing agent such as waste gypsum is added to the slurry thus coagulated, the slurry has a dispersed particle structure. In addition, the addition of a flocculant to the dispersed slurry changes the dispersed particle structure into a particle structure in which attractive force is generated again. However, the grain structure created by the new interparticle attraction is not a cohesive grain structure, and unlike the mesh structure of the initially coagulated particles, the grain structure is easily rearranged by weak stress. .

Coagulants used in the present invention include inorganic salts containing trivalent, divalent, or monovalent cations, and the addition of coagulants having this composition reduces the electrostatic repulsion by reducing the electrical double layer in the sludge. In other words, the mesh structure of the dispersed particles is converted into a mesh structure in which attraction is generated by continuous van der Waals attraction.

In addition, the first minimum of the potential wells anticipated in the DLVO theory to produce a slurry of agglomerated structure is induced to a second minimum to form agglomerates with no attractive force. However, particles in such agglomerates do not generate strong touching between the particles.

According to the present invention, a slurry is dispersed by adding a peptizing agent containing waste gypsum, and a flocculant is added to a slurry in which particles are dispersed to form a cohesive network structure. A slurry having a structure is prepared. In other words, after adjusting the electrostatic repulsive force by using a peptizing agent, by forming a mesh of particles by controlling the attraction force by using a flocculant, using a gelation of the slurry to prepare a porous slurry with a constant pore size distribution. That is, if the slurry is dispersed by maximizing all the electrostatic repulsive potentials and then placed at the second minimum value of the potential wells using hydration repulsion and van der Waals attraction (see US Pat. No. 5,188,780), Non-touching network (non-touching network) but weak compared to the meshed network structure is easy to redistribute by stress.

The principles of various types of organic and inorganic salts can be applied to enhance the coagulated particle network due to the hydration repulsion of charged ceramic particles. However, in the case of applying organic salts, an additional process for removing organic matter is inadequate in terms of simplifying the process, and depending on the composition of the fine ceramic particles, in some cases, a special type of salt is likely to react with the ceramic particles. It would be inappropriate. For example, inorganic salts such as NaCl or NH ₄ Cl and the like are suitable for use with most ceramic powders.

According to the present invention, it is possible to produce a slurry in which a flocculant forms a network structure of particles having a weak attraction force, and does not settle due to the gelation of the network structure. First, alumina (Al ₂ O ₃ ) and silica (SiO ₂ ) are included in about 250 to 550 parts by weight of at least one non-plastic first powder composed of a solid waste containing aluminosilicate as a main component such as coal ash, stone powder or incineration ash. A slurry having a composition of about 100 to 250 parts by weight of a plastic second powder composed of clay, kaolin, pottery stone, or mica mineral is prepared.

Subsequently, about 1 to 30 parts by weight of a peptizing agent is added to the slurry to make a dispersed slurry (mixture of water and powder), and then a slurry is added by adding a coagulant containing about 5 to 15 parts by weight of waste gypsum. Particles contained in the attraction force with other particles to form agglomerates, and a porous slurry is prepared by magnetic gelation of PSHP between these agglomerates. At this time, the peptizing agent comprises Na ₂ SiO ₃ , Na ₄ P ₂ O ₇ or Na ₂ CO ₃ , The flocculant Al ³⁺ , Mg ²⁺ , Sr ²⁺ , Ba ²⁺ , Ca ²⁺ , Inorganic salts containing any one or more of Li ⁺ , K ⁺ or Na ⁺ .

In the present invention, it is preferable that the first non-plastic powder contains coal ash, and the second plastic powder preferably contains clay. In addition, the peptizing agent is preferably comprising a Na ₂ SiO _3, the coagulant preferably includes a pyeseokgo. Table 1 shows the results of analyzing the chemical composition of the slurry comprising the first powder, the second powder and the flocculant according to the present invention.

SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO Na ₂ O K ₂ O TiO ₂ P ₂ O ₅ SO ₃ Ig-loss clay 61.67 22.74 3.49 0.61 0.48 0.42 1.57 0.29 0.05 ㆍ 8.67 Coal ash 65.28 22.87 3.93 0.85 0.55 0.24 0.91 1.22 0.25 ㆍ 3.82 Waste gypsum 1.98 0.7 0.11 31.66 ㆍ ㆍ ㆍ ㆍ ㆍ 46.95 20.32

When the content of the non-plastic first powder in the slurry is less than about 10 weight percent, properties such as strength and abrasion resistance are lowered, and when the content of the first powder exceeds about 70 weight percent, particles in the slurry are stably added. The problem of not being distributed appears. In addition, when the content of the second plastic powder in the slurry is less than about 30% by weight, it is difficult to produce a slurry due to the aggregation of particles, and when the content of the second plastic powder exceeds about 90% by weight, the non-plasticizer The problem arises that the characteristics of one powder are not expressed at all.

When the peptizing agent is added in less than about 0.1 parts by weight with respect to about 100 parts by weight of the slurry, there is a problem that the particles are not dispersed due to insufficient amount of adsorption on the surface of the solid particles in the slurry, When the amount exceeds about 10 parts by weight, the electrolyte concentration in the slurry becomes high so that the particles are not dispersed, and the amount of the liquid phase becomes too large when the molded body is sintered, resulting in a deformation of the ceramic sintered body.

The flocculant includes waste gypsum based on CaSO ₄ , which is generated in large quantities in a desulfurization process, phosphoric acid, hydrofluoric acid, boron, titanium, and the like. At this time, when the flocculant is added in an amount of less than about 0.01 part by weight with respect to about 100 parts by weight of the slurry, there is a problem that the aggregation of the particles does not occur smoothly, when the content of the flocculant exceeds about 2 parts by weight Due to the difficulty in controlling the size of the aggregate, the size of the aggregate becomes so large that the aggregate settles, making it difficult to manufacture a ceramic porous body having a uniform pore size.

According to the present invention, the slurry is peptized using a peptizing agent, and then divalent ions are added to the peptized slurry as a coagulant, thereby reducing the electric double layer in the slurry to increase the viscosity, and using the gelation of the slurry to fine-tune the slurry. By adjusting the structure, it is possible to produce a ceramic porous body having a uniform pore structure. In general, according to the Hofmeister series, the aggregation effect of SO ₄ ^2- is the largest in the case of anions, and the larger the ionic value and the smaller the ion radius, the larger the aggregation effect. Accordingly, in the present invention, waste gypsum containing CaSO ₄ as a main component, which is generated in large quantities in a desulfurization process or a manufacturing process such as phosphoric acid or hydrofluoric acid, is used as a flocculant. The addition of the coagulant containing waste gypsum to the dispersed slip produces the same effect as the concentration of the electrolyte increased according to the Schultz-Hardy rule, reducing the electrical double layer in the slip, resulting in coagulation of particles. ), The viscosity of the slurry gradually increases.

Hereinafter, a method of manufacturing a ceramic porous body having continuous pores according to preferred experimental examples of the present invention will be described in detail, but the present invention is not limited or limited by the following experimental examples.

Experimental Example 1

300 parts by weight of coal ash, the first powder having a non-plasticity, and 120 parts by weight of clay, the second powder having a plasticity, were mixed to form a mixture, and then the mixture of the first powder and the second powder was uniformly dispersed in 250 parts by weight of water. To prepare a slurry. At this time, the slip specific gravity was about 1.60 g / cm 3.

Subsequently, water glass containing Na ₂ SiO ₃ as a peptizing agent was continuously added to the slurry from about 1.0 part by weight to about 30 parts by weight in about 5 parts by weight. At this time, the viscosity change of the slurry was measured at about 20 rpm for about 15 seconds using a viscometer (Brookfield viscometer DVII +). As the amount of peptizing agent increased, the viscosity of the slurry gradually decreased, but when it reached a certain value, the viscosity did not decrease any more, and the viscosity was about 200 cP.

The slurry was aged for about 24 hours, and then the viscosity of the slurry was measured using a viscometer while adding waste gypsum containing CaSO ₄ as a flocculant to 13 parts by weight from 7 parts by weight to about 0.5 parts by weight. Measured by. When the amount of flocculant in the slurry was increased so that the viscosity of the slurry was about 1000 to 1500 cP, a molded article was prepared by injecting into a mold having a standard of about 20 Φ × Ohm / m.

After the molded article was naturally dried for about 12 hours, the first dried molded article was put into a freeze dryer. The molded body was secondly lyophilized for about 48 hours at a temperature of about -20 ° C in a freeze dryer, and then dried for about 24 hours at a temperature of about 100 ° C in an electric oven to completely dry the molded body. In this case, the total drying time of the molded body was about 84 hours.

Next, the dried molded body was put into an electric furnace, and the molded body was sintered by raising the temperature of the electric furnace to about 1150 ° C at a temperature rising rate of about 10 ° C / hr and maintaining it for about 2 hours. After the sinter was formed in the electric furnace, the sinter was cooled in the electric furnace.

As shown in FIG. 1, in the case of the molded body and the sintered body prepared from the slurry having a specific gravity of about 1.60 g / cm 3, the apparent porosity was about 48.9% and about 43.2% percent, respectively, and thus, it was confirmed that the ceramic porous body was possible. . Most of the pores of the molded body and the sintered body had a particle diameter of about 4 ~ 10㎛, it was possible to manufacture a ceramic porous body having continuous pores.

Experimental Example 2

350 parts by weight of coal ash, the first powder having a non-plasticity, and 150 parts by weight of clay, the second powder having a plasticity, were mixed to form a mixture, and then the mixture of the first powder and the second powder was uniformly dispersed in 300 parts by weight of water. To prepare a slurry. At this time, the slip specific gravity was about 1.55 g / cm 3.

In the present experimental example, the manufacturing process of the ceramic porous body including the content of the peptizing agent and the coagulant added to the slurry and subsequent molding and sintering is the same as in Example 1 described above. In drying the molded article, first, the molded article was naturally dried for about 12 hours, and then the first dried molded article was put into a freeze dryer. The molded body was lyophilized for about 60 hours in a vacuum at a temperature of about -20 ° C and then dried for about 24 hours at a temperature of about 100 ° C in an electric oven to completely dry the molded body. At this time, the total drying time was about 96 hours.

As shown in FIG. 1, the apparent porosities of the sintered bodies of the molded bodies produced according to the present examples were about 58.5% and about 52.1%, respectively.

Experimental Example 3

500 parts by weight of coal ash, which is the first powder, and 200 parts by weight of clay, which is the second powder were mixed to form a mixture, and then a mixture of the first powder and the second powder was uniformly dispersed in 350 parts by weight of water to prepare a slurry. At this time, the slip specific gravity was about 1.65 g / cm 3.

In the present experimental example, the manufacturing process of the ceramic porous body including the content of the peptizing agent and the coagulant added to the slurry and subsequent molding and sintering is the same as in Example 1 described above.

After the molded article was naturally dried for about 12 hours, the first dried molded article was put into a freeze dryer. The molded body was lyophilized for about 36 hours in a vacuum at a temperature of about -20 ° C for about 36 hours, and then dried in an electric oven at a temperature of about 100 ° C for about 24 hours to completely dry the molded body. At this time, the total drying time was about 72 hours.

As shown in Fig. 1, the apparent specific gravity of the sintered compact of the molded article produced according to this embodiment was about 43.2% and about 37.4%.

Experimental Example 4

A slurry was prepared by mixing 550 parts by weight of coal ash, which is a non-plastic powder, and 250 parts by weight of clay, a second powder, having a plasticity, and then uniformly dispersing the mixture in 350 parts by weight of water. At this time, the specific gravity of the slurry was about 1.68 g / cm 3. In the present experimental example, the manufacturing process of the ceramic porous body including the content of the peptizing agent and the coagulant added to the slurry and subsequent molding and sintering is the same as in Example 1 described above.

After the molded article was naturally dried for about 12 hours, the first dried molded article was put into a freeze dryer, and freeze-dried for about 36 hours at a temperature of about −20 ° C. in a vacuum. Subsequently, the molded product was completely dried by drying for about 24 hours at a temperature of about 100 ° C. in an electric oven. In this case, the total drying time was about 72 hours.

Referring to Figure 1, the apparent specific gravity of the sintered compact of the molded article produced according to this embodiment was about 41.7% and about 36.5%.

According to the present invention as described above, it is possible to produce a ceramic porous body having a plurality of continuous uniform pores. Such a ceramic porous body can be applied as a ceramic filter or a ceramic carrier.

In addition, according to the present invention, by adjusting the fine structure of the slurry, it is possible to easily control the characteristics and the size of the pores of the molded or sintered body produced from such a slurry.

Furthermore, according to the present invention, since the ceramic porous body is manufactured by inducing peptizing and agglomeration of the slurry using a peptizing agent and a coagulant made of inorganic matter, not an organic additive as in the conventional case, a separate organic matter removing process is not required. The simplicity and economy of the process can be achieved while producing environmentally friendly ceramic products.

In particular, according to the present invention, since waste gypsum generated in a desulfurization process, phosphoric acid, hydrofluoric acid, boron, or titanium manufacturing process can be recycled as a coagulant to produce a ceramic product, it contributes to environmental problems and at the same time produces a ceramic product. Can be significantly lowered.

While the above has been described in detail with respect to the preferred experimental examples of the present invention, the present invention is not limited by the above experimental examples, the present invention without departing from the gist of the invention claimed in the following claims Anyone with ordinary knowledge in the field will be able to make various changes.

1 is a graph measuring the apparent porosity of a molded body and a sintered body manufactured using a freeze-drying method by magnetic gelation according to the present invention.

Claims (2)

Forming a mixture by mixing 250 to 550 parts by weight of the first powder of the solid waste having non-plasticity and 100 to 250 parts by weight of the second powder having the plasticity; Adding 200 to 400 parts by weight of water to the mixture to form a slurry; Adding 1 to 30 parts by weight of a peptizing agent to the slurry to form a dispersed slurry; Adding 5 to 15 parts by weight of a flocculant to the dispersed slurry to form agglomerates; Forming a molded body by magnetic gelation of the aggregate; Drying the molded body for 10 to 15 hours by using a freeze drying method of freeze drying for 30 to 65 hours at a temperature of -25 to -15 ° C in a freeze dryer; And A method for producing a ceramic porous body having continuous pores of about 4 ~ 10 ㎛ size comprising the step of sintering the molded body. delete