JPH0212899B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air-permeable porous body and a method for producing the same, and in particular uses natural and inexpensive raw materials such as siliceous waxite, limestone, and clay to reduce the amount of gas produced during the calcination reaction. The present invention relates to a high-performance air-permeable porous body with uniform pore diameters that can be obtained using glass phase and solid phase reactions, and a method for producing the same.

[Prior art] Ceramic porous bodies have been used as filters and aeration parts in a wide range of fields such as the food industry, water treatment, and aquaculture, by taking advantage of their breathability and chemical stability. It is put into practical use as

Conventionally available methods for manufacturing porous ceramic bodies can be classified according to their principles as follows.

Utilization of voids before firing Ceramic raw materials are mixed into polyurethane foam raw materials, formed into a foam, and then fired to remove the resin component.

Ceramic slurry is coated on polyurethane foam and fired.

The granular resin is packed, and the ceramic slurry is poured into the created space and fired.

Utilization of voids during firing process Stop sintering before the start of solution.

Calcination or addition of volatile substances.

A small amount of vitreous flux and a binder are added to aggregate particles with an adjusted particle size distribution and fired.

A porous raw material such as diatomaceous earth is mixed with a binder and fired.

Using glass phase separation (porous glass) Sol-gel method (silica gel, etc.) Utilizing intracrystalline voids (zeolite, etc.) The approximate pore radius range of porous bodies produced by these manufacturing methods is shown in Figure 1. Become.

[Problems to be solved by the invention] Among the conventional manufacturing methods for porous bodies, the method that utilizes voids during the firing process is most suitable for manufacturing porous bodies with pore radius of about 0.3 to 50 μm and which have various uses. However, with this method, it is difficult to obtain a high porosity, and the resulting porous body is brittle in terms of material and tends to have irregular pores. Further, although the method is a good method for producing porous bodies at a low cost, the porous bodies obtained by this method also tend to have irregular pore sizes and become brittle. This method is also not industrially advantageous, so conventionally,
Most of them are manufactured by this method.

However, in this method, the average particle size and particle size distribution of aggregates (porcelain shimoz, alumina, titania, silicon carbide, etc.) are adjusted, and as much as possible of vitreous flux (a material that binds aggregates during firing) is added. ) and a binder such as clay, which must be fired, requires a large number of manufacturing steps and has the disadvantage that porous bodies cannot be manufactured efficiently at low cost.

[Means and effects for solving the problems] The present invention provides an air-permeable porous body that has uniform pore diameters and can be manufactured at low cost, and such a porous body,
It does not require a classification operation to narrow the particle size distribution width of the raw material, and it uses inexpensive natural raw materials without using glassy flux or combustion materials (such as sawdust), and the glass phase generated during the firing reaction. The present invention provides a method for manufacturing using a sintering reaction, comprising: 70 to 88% by weight of SiO ₂ , 5 to 23% by weight of CaO;
An air permeable porous body characterized by containing 5-15% by weight of Al ₂ O ₃ and siliceous waxite, limestone and clay, 70-88% by weight of SiO ₂ , 5-23% by weight of CaO and Al ₂ O ₃ 5 The gist of the present invention is to provide a method for manufacturing a breathable porous body, which comprises blending and molding the mixture to a concentration of ~15% by weight, and firing at a temperature of 1000°C or higher.

That is, _the present invention was completed as a result of the following research on CaO- _Al2O3 - _SiO2- based tile substrates.

Ceramic tiles are a typical example of CaO−Al ₂ O ₃ −SiO ₂ ceramics. The approximate composition of this substrate is SiO ₂ 58-75% by weight, Al ₂ O ₃ 13-25% by weight,
CaO5-9% by weight (composition range is shown in I in Figure 2)
The raw materials are Rouseki (pyrophyllite, kaolin, Al ₂ O ₃ about 13% by weight or more), limestone, and clay. As an example of the range of Fig. 2, SiO ₂ 73
Figure 3 shows the apparent porosity and shrinkage of a formulation (hereinafter referred to as "Formulation A") having a composition of 20% by weight of Al ₂ O ₃ and 7% by weight of CaO. Further, as examples of those outside the range of I in Fig. 2, siliceous waxite (pyrophyllite, kaolin, about 13% by weight or less of Al ₂ O ₃ ), limestone, 74% by weight of SiO ₂ using clay, The shrinkage rate and apparent porosity of a formulation containing 12% by weight of Al ₂ O ₃ and 14% by weight of CaO (hereinafter referred to as "Formulation B") are shown in FIG. FIGS. 4a and 4b show the X-ray diffraction patterns of each formulation A and B, and FIGS. 5a and 5b show the pore size distribution of each formulation A and B at each firing temperature.

By considering these FIGS. 3 to 5, the following can be found.

That is, from FIG. 3, formulation B has a higher porosity and a lower shrinkage rate at temperatures below 1200°C.

From Figure 4, at 1000°C for both A and B formulations, gehlenite (2CaO・Al ₂ O ₃・SiO ₂ ), wollastonite (CaO・SiO ₂ ), anorthite (CaO・
(Al ₂ O ₃ .2SiO ₂ ) is generated, and in formulation A, as the firing temperature increases, gehlenite and wollastonite disappear, and a large amount of anorthite is generated. At the same time, mullite (3Al ₂ O ₃
2SiO ₂ ) and cristobalite (SiO ₂ ) are also increasing. On the other hand, in formulation B, gehlenite, wollastonite, and anorthite are produced similarly to formulation A, but the amount of wollastonite produced is large;
Once produced, these minerals tend to decrease as the firing temperature increases.

In addition, each symbol in FIGS. 4a and 4b indicates the following.

Q...Quartz, C...Calcite, F...Felspar, M...Mullite, P...Pyrofluorite, G...Gerenite, Cr...Cristobalite, W...Wollastonite, α-W... α
-Wollastonite, A...Anorcite.

Generally, with compositions in the range shown in Figure 2, such as formulation A, temporary expansion occurs during the formation and disappearance of gehlenite and wollastonite, which increases the porosity and reduces the shrinkage rate. Although this is known (in interior ceramic tiles, this property is utilized to improve dimensional accuracy), temporary expansion occurs in the B formulation as well, increasing the porosity. As shown in Figure 5, the pore diameter increases as the firing temperature increases, but compared to formulation A, formulation B has the characteristic that as the pore radius increases, the pore size distribution becomes more uniform. I understand.

That is, in formulation B, CaO and pyrophyllite produced by the decomposition of limestone (CaCO ₃ ), Al ₂ O ₃ produced by the decomposition of kaolin mineral, and gehlenite, wollastonite, and anorthite produced by reacting with _{the two} SiO components disappear. As a result, a eutectic reaction shown at point E in Figure 2 partially generates a liquid phase with a low melting point, which causes quartz (SiO ₂ ) particles in the siliceous waxite (partially transformed to cristobalite) particles. It is presumed that a porous body with extremely uniform pore diameters was formed due to the combination of the pores. On the other hand, in Formulation A, since a large amount of anorsite, which is a reaction product, remains, it is thought that the eutectic reaction is difficult to occur, resulting in an irregular pore size distribution.

In order to find a range that tends to be similar to the B formulation, the present inventor conducted formulation tests of various compositions using siliceous waxite, limestone, and clay, and as a result, the following findings were obtained.

(i) For compositions near point E in Figure 2, the eutectic reaction rapidly progresses at temperatures above 1100°C and the porosity decreases.

(ii) With a composition close to point D, a product with high porosity was obtained, but it was difficult to make the pore diameter uniform and the product was likely to be brittle.

(iii) If the composition is close to point F, the porosity is small and it is difficult to make the porosity uniform.

(iv) When it comes close to SiO ₂ , high porosity can be obtained but it tends to become brittle.

Based on the above knowledge, as a result of various studies,
_SiO2 70-88% by weight, _CaO5-23 % by weight and _Al2O35
~15 wt%, especially in terms of porosity, pore uniformity, and brittleness, _SiO2 70-80 wt%, CaO10-23
It has been found that the best range is 5 to 15% by weight of Al ₂ O ₃ , ie, the range shown in FIG.

Therefore, the composition of the breathable porous body of the present invention is as follows:
_SiO2 70-88% by weight, _CaO5-23 % by weight and _Al2O35
~15% by weight and its pore diameter is 0.3~50μ
m is extremely uniform.

Therefore, the air-permeable porous body of the present invention is made of siliceous waxite, preferably pyrophyllite and/or kaolinite, which is a natural raw material and is supplied at low cost, and has an Al ₂ O ₃ content of about 13% by weight or less. SiO ₂ 70-88% by weight, using limestone and clay as starting materials;
A composition containing 5 to 23% by weight of CaO and 5 to 15% by weight of Al ₂ O ₃ is prepared, and if necessary, a molding aid such as an organic binder is added, and the molded product is molded by a conventional method.
By firing at a temperature of 1000°C or higher, a gas-permeable porous body with uniform pore diameter can be easily produced by the liquid phase and solid phase reactions that occur during the firing reaction.

By the way, the pore diameter of the porous body is closely related to the particle diameter and particle diameter distribution of the starting material. As a result of tests conducted by the present inventor, it was found that the closer the particle size distribution of siliceous rouseki and the particle size distribution of limestone, the more uniform the pore diameter of the fired body tends to be. Therefore, by adjusting the siliceous waxite particle size distribution and the limestone particle size distribution to arbitrary particle sizes, a porous body with a desired constant pore diameter can be obtained. According to the starting materials used in the method of the present invention, those obtained by normal ball mill polishing can be used as they are without performing any classification operation to obtain the desired particle size.

[Example] Examples will be described below.

Example 1 A porous body was manufactured by the method of the present invention. The particle size distribution of the raw materials used was measured by Sedigraph, a sedimentation method, and the results are shown in FIGS. 6a to 6c.

The siliceous rouseki used was one that had been ground for 6 hours in a ball mill (as shown in Figure 6a), 9 hours (see the same figure), and one that had been ground for 9 hours in a stirring mill for an additional 6 hours (see Figure 6a). there was. For limestone, ball mill 6-hour fine polishing (Figure 6b) and 9-hour fine polishing (the same)
The same product was used after being polished for 9 hours and then further polished for 6 hours using a stirring mill.

As for the clay, used was a watermelon clay (commercially available product, shown in Figure 6c) which had been polished for 6 hours using a stirrer mill (same as above).

Using raw materials with the particle size distribution shown in Figure 7, siliceous Rouseki
After mixing slurry with a ratio of 70.2% by weight, 22.1% by weight of limestone, and 7.7% by weight of clay, it was dried, and after adding 0.7% by weight of PVA, it was press-molded at 300 kgf/cm ² with a water content of 7% by weight. Firing was carried out in an electric furnace at a rate of 7° C./min, maintained at the maximum temperature shown in FIG. 7 for 1 hour, and then naturally cooled in the furnace.

The composition of the porous body is 14.0% by weight of CaO, 74% by weight of SiO ₂ , and 12% by weight of Al ₂ O ₃ .

The pore distribution of the obtained porous body is shown in FIG.

Furthermore, the amount of air permeation per unit area and unit thickness of these porous bodies is shown in FIG.

From FIGS. 7 and 8, it is clear that according to the present invention, a highly air permeable porous body having uniform pore diameters can be manufactured using inexpensive raw materials.

Example 2 One side of a siliceous waxite-limestone-clay fired body at 1200°C was impregnated with a slurry of siliceous roastite-limestone-clay and re-fired at 1000°C to produce a porous body with a two-layer structure.

Figure 9 shows the amount of air permeation through the obtained two-layer structure porous material, impregnated siliceous waxite-limestone-clay 1
The amount of air permeation is shown for the 1000°C fired body of the layer and the 1200°C fired body of siliceous waxite-limestone-clay as the base material.

From FIG. 9, it is clear that according to the present invention, by adopting a two-layer structure, a porous body with lower pressure loss can be obtained even with the same pore diameter.

[Effects of the Invention] As detailed above, the breathable porous body of the present invention has the following features:
_SiO2 70-80% by weight, _CaO5-23 % by weight and _Al2O35
~15% by weight, e.g. pore diameter 0.3-50μm
It has extremely uniform pore diameters and is highly breathable, making it extremely useful as a filter or aeration member.

Therefore, such an air-permeable porous body of the present invention can be efficiently manufactured at low cost by the method of the present invention using inexpensive natural raw materials such as siliceous waxite, limestone, and clay.

The porous body according to the present invention produces cristobalite when fired, so it cannot be used at high temperatures of 200°C or higher and is used at room temperature. However, it can be used in the food industry, water treatment, aquaculture, etc. There is no problem in using it as a filter or as an aeration member.

[Brief explanation of drawings]

Figure 1 is a diagram showing the pore radius range of a porous body produced by a conventional method, and Figure ₂ is a diagram showing _the pore radius range of a porous body produced by a conventional method _.
System phase equilibrium diagram, Figure 3 is a graph showing the relationship between apparent porosity and shrinkage rate and firing temperature for formulations A and B, and Figures 4a and b are powder X-ray diffraction patterns for formulations A and B, respectively. Figures 5a and b are graphs showing the pore size distribution of formulations A and B, respectively; Figures 6a, b, and c are graphs each showing the particle size distribution of the raw materials used in Example 1; FIG. 7 is a graph showing the pore distribution of the porous body obtained in Example 1, FIG. 8 is a graph showing the air permeation amount of the porous body obtained in Example 1, and FIG. It is a graph showing the air permeation amount of the obtained two-layer structure porous body and each layer structure porous body.

Claims (1)

[Claims] 1 SiO ₂ 70 to 88% by weight, CaO 5 to 23% by weight, and
A breathable porous body characterized by containing 5 to 15% by weight of Al ₂ O ₃ . 2. The breathable porous body according to claim 1, wherein the porous body has a pore diameter of 0.3 to 50 μm. 3 Siliceous waxite, limestone and clay, SiO ₂ 70~88
wt%, CaO5-23 wt% and _{Al2O3 5-15} wt%
1. A method for producing a breathable porous body, which comprises mixing and molding the materials so that the following results are obtained, and firing the materials at a temperature of 1000°C or higher.