KR100530104B1 - Method for manufacturing ceramic porous bodies reutilizing solid-state wastes - Google Patents

Abstract

The present invention relates to a method for producing a ceramic porous body having a uniform pore size distribution by dispersing and then reaggregating ceramic powder using water as a dispersion medium, and more particularly, from the group consisting of a solid waste having aluminosilicate as a main component. 0.1 to 10 parts by weight with respect to 100 parts by weight of a slurry having a composition of 10 to 70% by weight of one or more non-plastic powders selected and 30 to 90% by weight of one plastic powder selected from the group consisting of clay, kaolin, stone and mica minerals. It relates to a method for producing a ceramic porous body having a uniform pore structure by adding a peptizing agent and 0.01-2 parts by weight of a flocculant. The method for producing a porous body according to the present invention does not require an organic material removal process using an inorganic peptizing agent and a coagulant, but not an organic additive, so there is no problem in the environment, and it is possible to work at room temperature, so that workability is good, and the process is simplified. It is also economically favorable.

Description

METHOD FOR MANUFACTURING CERAMIC POROUS BODIES REUTILIZING SOLID-STATE WASTES

The present invention relates to a method for producing a ceramic porous body having a uniform pore structure, and more particularly, to a ceramic porous body having a uniform pore structure by appropriately adding a peptizing agent and a coagulant to the non-plastic powder and the plastic powder. It relates to a method of manufacturing. The method of the present invention generally relates to an optimum dispersion method and a molding method in a medium of ceramic particles to be applied.

As a method of molding conventional ceramic materials, techniques such as injection molding, tape casting, and plastic extrusion are widely known, but these techniques are dispersed together with an organic binder and a plasticizer. Organic solvents have been used to facilitate the shaping and manipulation of the granulated particles. Therefore, the above methods require an organic solvent removal process during the process, and shrinkage and warpage may occur differently from the desired shape during the removal process. Due to the impurities remaining after the process, the mechanical properties of the ceramic may be degraded. Therefore, in consideration of environmental conditions and economic aspects, a new molding method without using an organic solvent or a polymer additive is required.

Powder processing of a general ceramic formed body is performed in the following four steps.

1) Preparation of Powder

2) Preparation of Powder (Slurry) for Molding

3) molding to the required shape

4) Eliminate pores and enhance densification and microstructure for optimal properties.

In each of the above steps, the nonuniformity of the ceramic formed body may be derived from the preparation of the powder itself and the powder (slurry), or may occur in the densification and filling process.

In addition, a coagulant is a main heterogeneous substance in powder including organic substance and inorganic substance. Stress is concentrated in each inhomogeneity, thus creating a potential flow, which leads to premature cracking, resulting in insulation and mechanical defects.

The method of the present invention is for controlling heterogeneity of microstructures and uncontrolled phase distribution. Thus, there is a need for a method that relies on an optimal process to minimize homogenization and uncontrolled phase distribution.

In order to improve the known methods for preparing ceramic substrates, considerable consideration should be given to the interaction properties between the ceramic powder particles suspended in the liquid medium. Because the behavior varies depending on the interaction between the particles, it is important to understand the structure of the slip due to the interaction between the particles in the slurry. Recently, Young, Graule and Lange have been actively researching new molding methods, but none of them have solved the problem of using organic solvent.

Young et al. [J. Am. Ceram. Soc. 74 (3) 612-618 (1991) studied gel-casting of alumina powders. The slurry was dispersed using an aqueous solution containing a polymer dispersant, and organic monomers were dispersed in the dispersed slurry. Monofunctional and bifunctional) were added and a catalyst was used to form macromolecules of macromolecules to fix the particles and raise the temperature of the slurry to form using gelling of the polymer. However, the method starts gelation after a certain time (idle time, idle time) after molding, in particular, the drying process of the molded body and the removal process of the binder is required, the process time can be prolonged, which may cause economic problems. have. Graule et al. [Ceramic Transaction, Vol 51, 457-467 (1994)] described an electric double layer by adjusting the pH of ceramic suspensions dispersed with acids, bases, and organic dispersants to an isoelectric point (IEP) or by adding organic salts directly to the suspension. The direct coagulation casting (DCC) method of aggregating by reducing the thickness of the present invention has been proposed. In this method, since the amount of organic salt is added and the coagulation rate varies depending on the temperature of the slurry, the temperature of the slurry must be controlled. There is a problem that idle time is required.

Lange et al. [US Pat. No. 5,188,780 (1993)] adjusted the pH of the suspension to disperse, disperse, re-disperse, and then molded by pressure filtration and centrifugation to produce a molded body, the method is based on the content of the solid It is said to be advantageous for forming the structural material because it has a microstructure of a nearly constant molded body regardless. However, the above method is a method capable of obtaining a compact molded body, but is not suitable for producing a porous molded body, and has a disadvantage in that the process up to producing the molded body is complicated.

Therefore, the present inventors have extensively studied a method of eliminating the drawbacks of the prior art and simplifying the process to disperse and agglomerate slurry, and to self-gellation by poly-silicon hydroxoprecipitates (PSHP). A method for enabling gelling molding has been developed, and the present invention has been completed based on this method.

Accordingly, an object of the present invention is to provide a method for producing a ceramic porous body having a uniform pore structure.

The method of the present invention for achieving the above object is one or more selected from the group consisting of 10 to 70% by weight of one or more non-plasticized powders selected from the group consisting of solid waste whose main component is alumina silicate and clay, kaolin, stone and mica minerals. 0.1 to 10 parts by weight of a peptizing agent and 0.01 to 2 parts by weight of a flocculant are added to 100 parts by weight of a slurry having a composition of 30 to 90% by weight of the plastic powder. There is this.

The peptizing agent may be Na ₂ SiO ₃ , Na ₄ P ₂ O ₇ or Na ₂ CO ₃ and the like, the flocculant Al ³⁺ , Mg ²⁺ , Sr ²⁺ , Ba ²⁺ , Ca ²⁺ , Li ⁺ And inorganic salts containing ions such as K ⁺ or Na ⁺ .

In order to achieve the above object, the present invention is to adjust the surface energy is lowered by adsorbing a peptizing agent to the surface of the highly charged ceramic particles in an aqueous medium to disperse the ceramic particles, the ceramic particles in the slurry is dispersed by adding a flocculant Small aggregates were formed and the gelation of these aggregates was used to form porous new network structures.

Therefore, when molding the desired article, there is no need for a separate molding method. In this new network structure, no sedimentation of particles in the slurry has ever been observed in the aggregated structure. Therefore, there is no great difficulty in producing a complicated shape.

Weak attraction between ceramic particles is caused by the combination of van der Waals attraction and electrostatic repulsion at a certain distance by DLVO theory with a very short range (less than 5 nm) of hydration repulsion. In this short range, hydration repulsion prevents the attraction of particles into contact. Thus, under moderate conditions, this force has a higher packing density when the dried powder or particles form contacted nets when the particles slip easily to other particles and solidify. Hydration repulsion is a repulsive force acting only when the distance between particle surfaces is very short (less than 5 nm), and van der Waals attraction becomes stronger [Ceramic Transaction, Vol. 22, 185-201 (1991)]. FIG. 1 is a schematic diagram showing three network structures between existing particles, in which (a) is a coagulation structure (contact mesh), and (b) a dispersion structure (non-contact mesh). And (c) represents an aggregate structure (non-contact mesh).

In the present invention, to prepare a ceramic porous body, using a slurry in which one or more non-plasticized powder selected from the group consisting of solid waste such as coal ash, powdered ash, incineration ash, and plastic powder composed of clay, kaolin, pottery stone and mica minerals are properly mixed. Since these particles, for example, the coal ash and clay particles, are hydrophobic in their surface, as described in DLVO theory, the particles are initially strongly coagulated in the slurry, and a mesh is formed between the coagulated particles. The sedimentation of the field occurred. When the peptising agent was added to the coagulated slurry, the slurry had a dispersed particle structure. Also, when a coagulant was added to the dispersed slurry, the dispersed particle structure was changed into a particle structure in which attractive force was generated. However, the grain structure produced by the new interparticle attraction is not a grain structure with strong cohesion. Unlike the network structure of the initially coagulated particles, the particles of the mesh were easily rearranged by the slight stress.

The flocculants used in the present invention are inorganic salts containing trivalent, divalent and monovalent cations, the addition of which results in reducing the electrostatic repulsion by reducing the electric double layer. In other words, the dispersed particle mesh has been transformed into a mesh structure that is attracted by continuous van der Waals attraction.

In order to prepare the slurry of the aggregated structure, the first minimum of the potential well expected in the DLVO theory was induced to a second minimum to form a non- attractive aggregate. However, the particles in these aggregates did not have strong touching between the particles, and the network structure of these particles is called a coagulated network [Ceramic Transaction, Vol. 22, 185-201 (1991) (FIG. 1 (c)). The method of the present invention adds a peptizing agent to disperse the slurry, and adds a flocculant to the slurry in which the particles are dispersed to form a coagulated mesh, PSHP self-gellation occurs in the formed mesh to form a slurry having a porous structure. In other words, it was possible to prepare a porous slurry having a uniform pore size distribution by controlling the electrostatic repulsive force using a peptizing agent, forming a mesh of particles by controlling an attractive force using a flocculant, and gelling the slurry.

That is, after dispersing the slurry by maximizing all the electrostatic repulsive potentials, and using the hydration repulsion and van der Waals attraction force to position the second minimum value of the potential well [US Patent No. 5,188,780 to Lang et al. (1993)] However, it is a non-touching network in which attractive force acts but is weaker than flocculated network, so it can be easily redistributed by stress.

The principles of various types of organic and inorganic salts can be applied to promote coagulated particle networks due to the hydration repulsion of charged ceramic particles. However, the application of organic salts is inadequate in terms of simplification of the process because the removal of organic matter is required, and in some cases, depending on the composition of the fine ceramic particles, it is inappropriate because a special type of salt may react with the ceramic particles. something to do. Inorganic salts such as NaCl, NH ₄ Cl and the like are preferred for use with most ceramic powders. The present invention forms a mesh of particles with weak attractive force by flocculant and does not cause sedimentation by gelation of such meshes. Slurry was prepared. This will be described in more detail as follows.

10-70% by weight of one or more non-plasticized powders selected from the group consisting of solid waste whose aluminosilicate is the main component and one selected from the group consisting of clay, kaolin, pottery and mica minerals comprising Al ₂ O ₃ and SiO ₂ 0.1 to 10 parts by weight of a peptizing agent was added to 100 parts by weight of a slurry having a composition of 30 to 90% by weight of a plastic powder of to form a dispersed slurry (a mixture of water and powder), and a slurry was added by adding 0.01 to 2 parts by weight of a flocculant. Particles included in the attraction to the other particles to form agglomerates, and a porous slurry was prepared using the magnetic gelation of PSHP between these agglomerates.

Here, the solid wastes include coal ash, stone powder, incineration ash, and the like. The preferred non-plastic powder of the present invention is coal ash, and the plastic powder is clay.

The peptizing agent is selected from the group consisting of Na ₂ SiO ₃ , Na ₄ P ₂ O ₇ and Na ₂ CO ₃ , preferably Na ₂ SiO ₃ , the flocculant Al ³⁺ , Mg ²⁺ , Sr ²⁺ , An inorganic salt containing one ion selected from the group consisting of Ba ²⁺ , Ca ²⁺ , Li ⁺ , K ⁺ and Na ⁺ , preferably CaSO ₄ .

The amount of the non-plasticized powder used in the present invention is 10 to 70% by weight, and if the amount is less than 10% by weight, there is a problem that the properties of the non-plasticized powders, such as strength and wear resistance, do not appear. If it exceeds 70% by weight, a problem arises in that a stable dispersed slurry cannot be produced. In addition, the amount of the plastic powder is 30 to 90% by weight, if the amount is less than 30% by weight, it is impossible to prepare a slurry, there is a problem without plasticity, if the amount exceeds 90% by weight of the non-plastic powder There is a problem that the characteristics are not expressed.

The peptizing agent of the present invention uses 0.1 to 10 parts by weight with respect to 100 parts by weight of the slurry of the present invention. If the amount is less than 0.1 part by weight, the amount of adsorption on the surface of the solid particles in the slurry may not be sufficient to disperse the problem. If the amount exceeds 10 parts by weight, the electrolyte concentration in the slurry becomes high, so that the dispersion is not possible, and the amount of the liquid phase during sintering causes too much deformation.

In addition, the flocculant of the present invention is used in an amount of 0.01 to 2 parts by weight based on 100 parts by weight of the slurry of the present invention. At this time, if the amount is less than 0.01 part by weight, there is a problem that aggregation does not occur. In addition, the aggregates are too large to cause sedimentation, and thus, the size of the aggregates is not controlled, and thus, it is impossible to prepare a porous body having a uniform pore size. The purpose of the present invention is to prepare a porous body having a uniform pore structure by adding phosphorus divalent ions to reduce the electric double layer to increase the viscosity, and to adjust the microstructure of the slurry by gelling the slurry. Hope Meister series (Hofmeister series) For the anion SO ₄ ^2- by a coagulation effect is the largest, positive ions are more ionic valency is less large ionic radius larger because the coagulation effect, in the present invention were selected for the CaSO ₄ as the coagulant, The addition of these flocculants to the dispersed slip produces the same effect as the concentration of the electrolyte, according to the Schultz-Hardy rule, resulting in coagulation as the electric double layer shrinks, thus increasing viscosity. Done.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

Examples 1-3

Coal ash and clay were mixed in a weight ratio of 7: 3 in the amounts shown in Table 1 and dispersed in water. Table 2 below describes the chemical composition of the coal ash and clay.

TABLE 1

TABLE 2

Viscosity change was measured after 15 seconds at 20 rpm with a viscometer (Brookfield viscometer DVII +) with 0.05% Na ₂ SiO ₃ added to the slurry.

Figure 2 is a graph showing the viscosity change according to the addition amount of the peptizer (water glass) to the slurry having a coal ash-clay composition of the present invention.

As the amount of peptising agent increased, the viscosity decreased, but if it exceeds a certain amount, the viscosity did not decrease any more, and the viscosity was about 200 cP. The slurry thus dispersed is defined as slip D, and the less dispersed coagulated slurry is defined as slip F, and the aggregated slurry that is coagulated again by adding a coagulant to the dispersed slurry slip D is defined as slip C.

After aging slip D for 24 hours, the flocculant CaSO ₄ was added in 0.01 wt% of the slurry by weight, and the viscosity was measured by the viscometer in the same manner as described above (Fig. 3), and the amount of the flocculant was increased to increase the viscosity to 1000 to 1500 cP. Upon arrival, it was injected into a frame of 20 ^φ × 0 ^h m / m and allowed to air dry.

Normally dry for 24 to 48 hours and then completely dry in 100 to 24 hours in a dryer. The dried molded body was heated up to 1150 ~ at a temperature increase rate of 10 ~ / hr in an electric furnace, and then maintained for 2 hours and cooled.

Figure 6a is a photograph showing a fired body made of the coagulated slurry of the present invention, Figure 6b is a photograph showing the fracture surface microstructure of the fired body made of the aggregated slurry of the present invention.

6a and 6b, the sintered compact thus prepared was measured by KS 3114 for volume specific gravity, and the microstructure was observed with a scanning electron microscope (Topcon SX-30E, Japan). In addition, the pore distribution of the molded body and the sintered body was measured by a pore size measuring instrument (Mercury poresizer 9320, Micromeritics, U.S.A) to investigate the size and distribution of the pores (Fig. 5).

In FIG. 2, the viscosity of the dispersed slurry (slurry with 2.8 wt% of crosslinking agent) is very low (Slip C, 200 cP in FIG. 2), which results in the behavior of a high repulsive particle network (FIG. 1). (B)). The viscosity of the flocced slurry (slip F, initial slurry, 1000 cP) is significantly higher than other slurries, with shear thining indicating that it is strongly cohesive, and a touching particle network. (A) of FIG. 1 [Ceramic Transaction, Vol. 22, 185-201 (1991)]. In addition, in the case of slurry specific gravity 1.6, when the amount of the peptizing agent is 3 parts by weight or more, the concentration of the electrolyte increases and the electric double layer is reduced, causing aggregation to settle and forming an unstable slurry. Was observed.

Referring to Figure 3, adding coagulant CaSO ₄ to the coal ash-clay slurry (slip D) dispersed by the addition of the peptizing agent increases the viscosity of the slurry (slip C), weakly attractive non-contact, cohesive mesh (C) of FIG. 1 is shown and share thinning behavior is shown. The rheological behavior of the flocculated slurry depends on the amount of flocculant CaSO ₄ added. That is, the viscosity increases exponentially as the amount of addition increases. However, when the amount of the flocculant is 0.05 parts by weight or more, the degree of aggregation becomes large and the viscosity of the floc rapidly increases, thereby reducing the flow of slip, making molding impossible. Therefore, the size of the newly formed mesh can be adjusted by adjusting the amount of CaSO ₄ added, and thus the result of controlling the size of pores in the slurry can be obtained.

Therefore, FIG. 1 (c) [Ceramic Transaction, Vol. 22, 185-201 (1991)], the particles in the agglomerated slurry are weakly fixed, and the gelling occurs as the peptising agent melts off the surface of the particles and the PSHP (Poly-Silicon Hydroxo Precipitate) is resorbed. In the case of slip weight 1.55 ~ 1.65, the volume specific gravity of sintered body is 1.31 ~ 1.49, so it shows that it is possible to manufacture porous body as satisfying the specific gravity specification of 1.3 ~ 1.8 of light weight aggregate.

5 is a graph showing the pore diameter distribution of the molded body and the fired body of the prepared test piece. Since the pore size distribution of the molded body and the sintered body showed a unimodal distribution of about 2.5 μm, aggregates were formed by the addition of divalent ions, and gelation of these aggregates occurred, and thus a porous body having a uniform pore distribution was possible. 6A is a photograph showing a fired body made of a coagulated slurry, and FIG. 6B is a photograph showing a fracture surface microstructure of the fired body made of agglomerated slurry.

6A and 6B, in the case of the coagulated slurry, it can be seen that the particle size and the pore size are not constant but large, and in the case of the aggregated slurry, the size of the aggregate is relatively small because it is a condition of reaggregation after dispersion. It is constant and it can be seen that the pore size is also small.

The general ceramic process has been made to remove the heterogeneity of particles and slurries. While the existing studies have generally focused on the study of particle filling and physical property enhancement, the present invention not only improves the homogeneity of ceramics, but also develops new molding methods. The purpose is to provide a new and innovative method in terms of controlling the microstructure of the slurry.

The method of the present invention does not require an organic matter removal process by preparing a porous body by inducing peptizing and agglomeration using inorganic peptizing agents and coagulants rather than organic additives, so there is no problem in the environment, and work at room temperature is possible. It is good and the process is simplified, which is very advantageous for the economy.

In addition, the method of the present invention is convenient and inexpensive, and can avoid the use of organic solvents, polymer binders, plasticizers, and the like, and is a safe method, and enables the production of ceramic substrates having a constant pore diameter distribution. Therefore, the present invention can control the microstructure as well as the complex form from a wide variety of ceramic powder. The present invention is expected to be able to manufacture the final ceramic product by making the required shape and microstructure using the inorganic material, and heat treatment.

1 is a schematic diagram showing three network structures between existing particles.

Figure 2 is a graph showing the viscosity change according to the amount of peptizer added to the slurry having a coal ash-clay composition of the present invention.

3 is a graph showing the viscosity change according to the addition amount of the flocculant (CaSO ₄ ) to the dispersed slurry of the present invention.

4 is a graph showing the bulk density of the molded and sintered bodies of the present invention.

5 is a graph showing the pore diameter distribution of the molded body and the fired body of the present invention.

Figure 6a is a photograph showing a fired body made of the tungsten slurry of the present invention.

Figure 6b is a photograph showing the fracture surface microstructure of the fired body made of the aggregated slurry of the present invention.

Claims (6)

Clay, kaolin containing aluminosilicate as a main component, 10 to 70 parts by weight of one or more non-plastic powders selected from the group of one solid waste selected from the group consisting of coal ash, lime powder and incineration ash, and Al ₂ O ₃ and SiO ₂ 0.1 selected from the group consisting of Na ₂ SiO ₃ , Na ₄ P ₂ O ₇ and Na ₂ CO ₃ with respect to 100 parts by weight of a slurry having a composition of 30 to 90 parts by weight of one plastic powder selected from the group consisting of pottery and mica minerals After dispersing the slurry by adding 10 parts by weight of a peptizing agent, Al ³⁺ , Mg ²⁺ , Sr ²⁺ , Ba ²⁺ , Ca ²⁺ , Li ⁺ , K ⁺ and Na ⁺ selected from the group consisting of A method for producing a ceramic porous body having a uniform pore structure, characterized in that the aggregate is formed by adding 0.01-2 parts by weight of a flocculant, which is an inorganic salt containing a cation, and formed by magnetic gelation of the aggregates. delete delete delete delete The method of claim 1, Method for producing a ceramic porous body having a uniform pore structure, characterized in that the pore size of the ceramic porous body is controlled by the amount of peptizing agent and flocculant.