JPS5842142B2 - Inorganic porous body and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inorganic porous body having excellent heat resistance, high strength, and chemical resistance.

In recent years, porous materials have been developed into a wide variety of types depending on their purpose.
Although they are made from a variety of materials and methods, they must be strong enough to withstand high temperatures, be chemically stable, and withstand loads and vibrations.

However, the porous materials that exist to date range from inorganic materials such as ceramics, glass, refractory materials, and inorganic fibers to various organic materials.
Either the constituent materials have low fire resistance, or even if they are fire resistant, the bonding material used to join them has low fire resistance, and the fire resistance as a whole is low.

There is also a porous body made entirely of high refractory material by adding burnt material or foaming agent to it and sintering it.
These are costly to produce and expensive.

Furthermore, as shown in FIG. 1, the state of pore formation is such that in addition to through holes, open pores or closed pores coexist, and the material is not an ideal porous body.

In addition, as a porous material for high temperatures, ceramic particles are fused at high temperatures of 1,350 to 1,800°C using a high-temperature flux, but they can withstand temperatures of 1,000°C or more and are chemically resistant. Although there are some, many have an insufficient bending strength (flexural strength) of less than 100 kg/d.

However, as shown in Figure 2, this product has ceramic particles 1' wrapped in high-temperature flux 2, and this high-temperature flux binds the ceramic particles together, so the strength of the product is low. It depends on the properties of the high-temperature flux, and the physical
Since the chemical properties are also similar, the ceramic granule nature contributes little to the properties of the product.

In this case, the diameter of the pores 1 is not constant due to the surface tension of the high temperature flux 2.

The present invention eliminates the drawbacks of such known porous materials, and has high heat resistance and
The purpose is to easily provide a high-strength inorganic porous body.

That is, the present invention provides a reaction layer in which inorganic particles selected from alumina, mullite, and cordierite are formed inside the inorganic particles by a reaction between the inorganic particles and a flux mainly composed of borosilicate glass frit. This is an inorganic porous material that is strongly bonded by chisel.

The material of the inorganic particles used in the present invention is appropriately selected from alumina, mullite, and cordierite depending on the purpose of the porous body.

In the case of a porous material that requires uniform pore size, use a spherical material with a uniform or fixed particle size distribution, and in the case of a porous material that requires a complicated flow path or an acute gap, Granules having a complex shape produced by crushing may be used by appropriately mixing coarse particles and fine particles.

Therefore, in the present invention, the inorganic granules are pulverized to an appropriate particle size and sieved in consideration of the required average pore diameter, passage amount, passage resistance, etc., and if necessary, the granules are placed in a ball mill or the like and rotated. It is used after processing, such as rounding the corners to make it almost spherical.

Alternatively, commercially available classified granules or granules already formed into a spherical shape may be used.

Such inorganic particles are strongly bonded directly to each other, ie, without using a medium.

To explain this using drawings, as shown in FIG. 3, a reaction layer 5 is formed inside the surface of the inorganic particles 1 during firing.
As a result, the inorganic particles 1 are firmly bonded to each other in the reaction sintering section 3.

Therefore, each of the pores 4 is a through-hole, and the shape of the through-hole is determined by the grain shape, resulting in a porous body with little pressure loss.

Further, since a sharp edge portion 6 is left in the through hole, when this is used as a furnace material, it has the effect of removing minute foreign matter floating in the fluid.

The present invention also relates to a method for manufacturing an inorganic porous body.

That is, the present invention provides inorganic particles selected from alumina, mullite, and cordierite with a flux mainly composed of borosilicate glass frit that reacts with the inorganic particles at a desired temperature to produce a new melt. 10-20% by weight
, after molding a mixture of 5% by weight or less of a binder and a small amount of water, at a temperature considerably higher than the melting temperature of the flux,
The present invention is also a method for producing an inorganic porous body, characterized in that firing is performed at a temperature below the temperature at which the essence of the inorganic particles melts and softens.

The flux used in the present invention is mainly composed of borosilicate glass frit as described above, and is preferably heated at a low temperature of 8.
It melts in the range of 00 to 1000°C, reacts with the essence of the inorganic particles, and forms a reaction layer that becomes softened at a temperature 300 to 500°C higher than the operating temperature of the porous body.

- For example, it is appropriate to add 15% by weight of clay and 5% by weight of titanium oxide to 80% by weight of frit with a melting temperature of 850°C for temperature adjustment.

In addition to such a flux, an organic binder is used in the present invention to provide green strength for easy handling during molding.

The binder is preferably one that is burnt out during firing, but has sufficient strength to handle the product during molding and drying; for example, CMC, PVA, etc. are suitably used.

Therefore, in order to produce the porous material of the present invention, inorganic granules are mixed with a fluxing agent, a binder, and water in a predetermined ratio, and thoroughly kneaded to coat the surface of the inorganic granules with the fluxing agent and binder. Coat evenly.

The appropriate amount of flux is 10 to 20% by weight based on the inorganic particles.

Temperature variations of less than 10% by weight reduce product strength.

If it exceeds 20% by weight, the residual content will accumulate between the inorganic particles,
As in the case of FIG. 2, the porosity is lowered and the edge portion 6 as shown in FIG. 3 disappears.

The binder is effective in small amounts of 5% by weight or less.

It is desirable that the amount of water be as small as possible to take advantage of the properties of the binder.

Molding is performed by a pressure method, a vibration method, etc., and the molded product can be in any shape such as a flat plate, cylinder, pot shape, or box shape. It is also possible to form a combination of the two.

When a molded product dries, its strength increases due to the binding agent, so
Now that it can be handled sufficiently, it is placed on a refractory table or in a container with refractory powder sprinkled on it, and then placed in a firing furnace and fired.

The firing temperature is 200 to 300°C higher than the melting temperature of the flux.

This temperature is below the temperature at which the essence of the inorganic particles melts and softens.

By firing, the flux melts on the surface of the inorganic particles, this melt wets the surface of the particles, and when the temperature reaches a higher temperature, it reacts with the inorganic particles on the surface to form a new compound.

In this state, there is no molten material between the particles, so the particles come closer to each other and are firmly bonded using the reaction layer as a boundary layer, and are bonded by a bonding force that is much greater than the fusion bond caused by the molten layer.

Therefore, much greater strength can be obtained from porous bodies produced by fusion bonding.

The pore size, porosity, and pressure drop of the porous body of the present invention can be controlled by adjusting the particle size of the inorganic particles.

Further, by selecting the inorganic particles and the flux, it is possible to produce a porous body that can be used at high temperatures.

For example, using a flux at 900℃ for fire-resistant inorganic particles1,
Products fired at 300°C can be used at temperatures of 1,100°C.

If a conventional porous material with a flux melted at 950°C has a temperature of 750°C,
°C is the maximum operating temperature.

The results are shown in FIG. 4 with a 1.5 kg/- hot load softening curve.

The solid line represents the present invention, and the dotted line represents the conventional example.

The flux in the present invention melts and reacts with the surface of the inorganic particles to become a high-temperature stable compound, so that it has chemical properties that are much more stable than those of a melted flux.

The present invention will be further explained below with reference to Examples and test results.

Example 1 Sintered mullite was pulverized as inorganic particles and sieved into second grades of 28-32 mesh (mullite-130) and 35-42 mesh (mullite Φ38).

Borosilicate glass (product name: +3244,
Nippon Ferro ■) 80% by weight, kaolin 15% by weight,
A material obtained by mixing and pulverizing 5% by weight of titanium oxide was used.

CMC was used as a binder, and the mixture was thoroughly mixed in the following proportions so that the surfaces of the particles were coated with the flux and binder.

Mixing ratio Inorganic granules 100 parts by weight Fluxing agent
20 parts by weight Binder 1 part Water 7 parts by weight This was pressure-molded in a mold at a surface pressure of 200 kg/i.
, and fired at 300°C to form a porous body.

For comparison, a porous body was formed by molding the same mixture and firing it at 950°C.

The test results of the above porous bodies are shown in Table 1.

Microscopic photographs (X50) of the products of Example 1 and Comparative Example using Mullite +38 are shown below.
5 and 6, respectively. In the case of FIG. 5, that is, the present invention, the form as shown in FIG.
In other words, it can be seen that the comparative example has a form as shown in FIG.

Such differences are manifested in differences in porosity and water permeability.

The bending strength of the product of the present invention is about 3.5 times higher than that of the comparative product, indicating that direct sintering between grains is highly effective.

When such a porous material is used as a filter at high temperatures, such as for filtering molten aluminum, it must be able to withstand use at a temperature of at least 750°C, must not be deformed or crushed, and must be free of particles. There should be no falling off.

Therefore, a hot load test was conducted and the results are shown in Table 2.

As is clear from the results in Table 2, a clear difference in hot strength was observed between Example 1 and Comparative Example.

Example 2 The present invention was prepared in the same manner as in Example 1, using as inorganic particles classified molten alumina that is close to spherical particles, sintered alumina that is known as irregularly shaped particles, and sintered mullite that is flat shaped particles. A porous body was made according to the method.

Table 3 shows the results of measuring each characteristic value.

In addition, for example, regarding sintered mullite porous bodies, acid resistance,
The alkali resistance was investigated by weight loss at 25°C for 1 hour, and the results are shown in Table 4.

As shown in the results in Table 4, in the case of the present invention, even when a flux is used, the elution loss is small, indicating that the presence of glass is rare.

In addition, when investigating this using X-rays, the 950°C fired product clearly shows the presence of a glass phase in addition to the mullite crystal peak, but the 1,300°C fired product shows a decrease in the glass phase. Inversely proportional to this, the peak of mullite crystals became higher, indicating that the number of mullite crystals was increasing.

As described above, the porous body of the present invention has high strength and excellent heat resistance and chemical resistance, so it can be used, for example, in compressor filters that require strength to receive pressure, refrigerant filters in refrigerators, and in applications that require high heat and pressure. It is useful as a porous body for filters, which is ideal for filters for molten metals and alloys.

[Brief explanation of the drawing]

Figures 1 and 2 show the state of pores in a conventional porous body, Figure 3 shows the state of pores in the porous body of the present invention, and Figure 4 shows softening under hot load of the product of the present invention and the comparative example. The curve, FIG. 5 shows a microscopic photograph of the product of the present invention, and FIG. 6 shows a microscopic photograph of the comparative example product. 1... Inorganic particles, 1'... Ceramic particles, 2... High temperature flux, 3... Reaction sintered part, 4, 4'. ...Kiko L5...Reaction layer, 6...Edge part.

Claims (1)

[Claims] 1. Inorganic particles selected from alumina, mullite, and cordierite are formed inside the inorganic particles by a reaction between the inorganic particles and a flux mainly composed of borosilicate glass frit. An inorganic porous material characterized by being strongly bonded only by a reaction layer. 2. 10 to 20 weight of a flux mainly composed of borosilicate glass frit that reacts with the inorganic particles at a desired temperature to produce a new melt is added to inorganic particles selected from alumina, mullite, and cordierite. %, a binder of 5% by weight or less and a small amount of water are mixed to form a bottom, and then heated to a temperature considerably higher than the temperature at which the flux melts, but below the temperature at which the essence of the inorganic granules melts and softens. 1. A method for producing an inorganic porous body, the method comprising firing an inorganic porous body. 3. The inorganic granules are polygonal complex granules obtained by crushing and sizing pre-sintered or melted inorganic materials, or spherical granules chemically or mechanically made into spherical shapes. A method for producing an inorganic porous body. 4. The method for producing an inorganic porous body according to claim 3, wherein the material of the inorganic particles is alumina, mullite, cordierite, or porcelain base. 5. The method for producing an inorganic porous body according to any one of claims 2 to 4, wherein the flux contains a frit. 6. The method for producing an inorganic porous body according to any one of claims 2 to 5, in which the flux is used in an amount of 10 to 20% by weight based on the inorganic particles.