JPH1087378A - Production of porous ceramic formed article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a porous lightweight heat resistant ceramic formed article at a low cost. SOLUTION: A ceramic stock compsn. contg. coal ash, an inorg. binder such as aluminum prim. phosphate or sodium silicate and a water-soluble alkali or alkali metallic halide, preferably sodium chloride as essential components or further contg. a hardening regulator such as alumina is preformed and fired at 300-600 deg.C to from a cermaic formed body. The water-soluble halide is then leached from the ceramic formed body by treatment with water or an aq. soln. to produce the objective porous lightweight ceramic formed body excellent in heat and sound insulating properties, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous ceramic molded product, and more particularly, to a method for effectively utilizing coal ash discharged as a large amount of industrial waste, and furthermore, has a high heat resistance. The present invention relates to a method for producing a porous ceramic molded product having good mechanical properties and excellent lightness at low cost.

[0002]

2. Description of the Related Art A large amount of coal is used as an energy source for thermal power generation, and a large amount of coal ash, which is the slag, is also discharged.

[0003] Among the coal ash, there is particularly fine fly ash. Fly ash is produced when pulverized coal is burned at a thermal power plant, etc., where coal ash is melted and rapidly cooled while being transported to the flue along with high-temperature combustion gas. It has become particles.
Since this has a self-hydrating action, some fly ash is used as fly ash cement.

[0004] Like flyland cement, fly ash cement sets by a hydration reaction. However, when heated to 500 ° C. or higher, water of crystallization in the cement condensate is released, and the mechanical strength is significantly reduced.

[0005] On the other hand, it is also known that coal ash is mixed with an inorganic binder such as Portland cement or water glass or an organic binder such as polyvinyl alcohol, and then sintered at a high temperature to obtain a ceramic-like molded product. Since this method requires a high sintering temperature, disadvantages in terms of energy are inevitable.

As a means for solving this problem, coal ash such as fly ash is mixed with a hardening modifier such as aluminum phosphate monobasic, water and aluminum oxide. There has been proposed a method of producing a ceramic molded article having excellent heat resistance, mechanical properties, and the like by firing at a low temperature (No. 14).
Inorganic Polymer Research Symposium).

According to this method, a dense ceramic molded article having good impact resistance is produced. However, for some uses such as certain building materials, a porous and lightweight ceramic molded article is required. ing.

[0008]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies to solve the above-mentioned problems, and have found that coal ash and an inorganic binder mainly containing aluminum monophosphate and the like are further required. When using a composition mixed with a curing regulator accordingly, at least one of a water-soluble alkali metal or alkaline earth metal halide such as sodium chloride is added to the composition, and at a specific temperature. After heating and sintering to form a ceramic molded article, this is treated with water or an aqueous solution to elute and remove the water-soluble halide from the molded article, thereby obtaining a porous lightweight ceramic molded article. We started and arrived at the present invention.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
A ceramic raw material composition is prepared by uniformly mixing at least one of coal ash, an inorganic binder, and a water-soluble alkali metal or alkaline earth metal halide, and then the composition is subjected to a predetermined process using a mold. After firing into a ceramic molded article at a temperature of 300 to 600 ° C., the water-soluble halide is dissolved and removed from the molded article with water or an aqueous solution to make the molded article porous. This is achieved by a method for producing a porous ceramic molded product, characterized in that

At this time, coal ash is added to a ceramic raw material composition comprising coal ash, an inorganic binder and a water-soluble alkali metal or alkaline earth metal halide, or a ceramic raw material composition further containing a hardening modifier. 10
It is preferable to mold with 0 to 40 parts by weight of water added per 0 parts by weight.

The above-mentioned inorganic binder includes a solid phase of primary aluminum phosphate (powder) or an aqueous solution containing primary aluminum phosphate, or a solid phase of sodium silicate or sodium silicate. Aqueous solution is preferably used. As the halide of the water-soluble alkali metal or alkaline earth metal, sodium chloride, calcium chloride, magnesium chloride or potassium bromide is used. Preferably, it is a 1 mm powder or crystal.

[0012] If necessary, the hardening regulator to be added to the ceramic raw material composition is preferably an oxide or hydroxide of at least one metal selected from aluminum, zinc, magnesium and calcium.

The mixing ratio of coal ash / inorganic binder / alkali metal or alkaline earth metal halide is 10 to 150 parts by weight of inorganic binder, 100 parts by weight of coal ash,
Alkali metal or alkaline earth metal halides 5
To 100 parts by weight, and when a curing control agent is added, the amount of the curing control agent should be 1
Preferably, the amount is 1 to 20 parts by weight based on 00 parts by weight.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As coal ash used in the method of the present invention, coal ash discharged from a thermal power plant or other factories is used. Among these coal ash, uniform and fine coal ash called “fly ash” is preferably used. This fly ash melts coal ash generated when pulverized coal is burned at a thermal power plant, and is rapidly cooled while being transported to the flue with high-temperature combustion gas. It became fine particles.

On the other hand, as the inorganic binding agent (binder), monobasic aluminum phosphate or a substance mainly composed thereof, or sodium silicate or a substance mainly composed of sodium silicate is used.

The first aluminum phosphate has the chemical formula: Al
_{2 O 3 · 3P 2 0 5} · 6H 2 O [ ie, Al (H ₂
P0 ₄₎ a water-soluble acid phosphate salt represented by _3],
In many cases, it is commercially available as an aqueous solution. However, in the present invention, the first aluminum phosphate is a solid phase first aluminum phosphate (for example, solid water) substantially free of water other than bound water (crystal water). Powdered primary aluminum phosphate)
Is preferred. The first aluminum phosphate in the solid phase has a function of expressing the hardening property of the coal ash by the reaction with the coal ash and the condensation by heating in the mixed composition, and has a function of converting the mixed composition into a ceramic. However, the method of the present invention is not limited to a solid phase, and a liquid containing a small amount of water can be used.

Further, sodium silicate has a chemical formula of Na ₂
A silicate represented by SiO ₃ , used as a powder or crystalline solid containing anhydrous or water of crystallization. Further, sodium silicate can be used in the form of an aqueous solution (usually called "water glass").

These inorganic binders (binders) may be used alone or in combination. If necessary, Portland cement or the like may be added to the above-mentioned inorganic binder.

Further, in the method of the present invention, in addition to coal ash and the above-mentioned inorganic binder, a curing regulator (solidification accelerator) can be used in combination, and usually it is preferable. As the curing regulator, oxides such as aluminum, magnesium, iron, zinc, boron, and calcium are suitable, and among them, alumina powder is particularly effective. Also, hydroxides such as aluminum hydroxide and calcium hydroxide are preferably used.

In the method of the present invention, the blending ratio (weight ratio) of each of the above components in the mixed composition for forming a ceramic is as follows: coal ash = FA, inorganic binder (aluminum monophosphate, sodium silicate) = P, When water-soluble halide (such as sodium chloride) = N and curing regulator (solidification accelerator) = C, the following ranges are appropriate. FA / P = 100 / 10-100 / 150 (preferably 100 / 20-100 / 100) FA / N = 100 / 5-100 / 100 (preferably 100 / 20-100 / 80) FA / C = 100/1 to 100/20 (preferably 100/5 to 100/10)

In the present invention, in addition to the above components, short fibers for reinforcement, whiskers, and the like can be mixed as necessary. Glass fiber, carbon fiber,
SiC fibers, aramid fibers, polyarylate fibers and the like are preferred. In addition, inorganic lightweight particles such as glass bubbles can be mixed to reduce the weight. The proportion of these additives is suitably 20% by weight or less based on the total weight (A + P + N + C) of coal ash (FA), inorganic binder (P), water-soluble halide (N), and curing regulator (C). It is.

In order to mix the above components, the above components are usually mixed well in a dry or wet system to obtain a homogeneous composition. Since the presence of a large amount of water in the mixing step adversely affects the porosity due to dissolution (elution) of the water-soluble halide, it is preferable to suppress the amount to 40 parts by weight or less per 100 parts by weight of coal ash. However, when a preform is prepared by press molding at a relatively low temperature such as ordinary temperature, a small amount (preferably coal ash 10) is used in order to maintain the shapeability of the molded product.
It is appropriate to have 10 to 30 parts by weight of water per 0 parts by weight.

This ceramic raw material composition is
0 to 180 ° C, preferably 80 to 100 ° C, for 5 minutes to
It can also be used by heating for 30 hours to form a preceramic. The form of the preceramic may be a powder or a pellet.

According to the method of the present invention, the ceramic raw material composition (including the case of preceramics)
After being placed in a molding die and subjected to pressure molding (press molding) at room temperature or under heating, the obtained preform is taken out of the mold or kept in the mold at 300 to 600 ° C, preferably 350 to 600 ° C. By firing at a temperature of 550 ° C., a ceramic molded article having toughness and excellent heat resistance can be obtained. Also, the ceramic raw material composition is put in a mold for molding, and 1 to 500 kg / cm ² , preferably 1 kg / cm ² .
A ceramic molded article can also be obtained by heating at the same temperature while pressurizing at a pressure of 0 to 500 kg / cm ² , but it is preferable to combine the former means.

That is, the ceramic raw material composition is placed in a mold for molding at room temperature or in a heated state at 1 to 500 K.
It is particularly preferred to form a preform by molding at a pressure of g / cm ² , followed by further firing at the above temperature,
For example, a ceramic raw material composition is placed in a mold for molding and pressed at room temperature under a pressure of 1 to 500 kg / cm ^{2 in} the presence of moisture, or 1 to 500 kg / cm ² under heating to 100 to 300 ° C. The preform obtained by hot pressing under pressure is taken out of the mold or kept in the mold, and is further heated and fired at 300 to 600 ° C. to be ceramicized, thereby having both improved mechanical properties and improved heat resistance. A ceramic molded product can be manufactured.
The firing time is suitably from 30 minutes to 30 hours.

In the above-mentioned pressure (press) molding, a known compression molding technique can be applied. For example, using a mold having a desired shape and dimensions, pressurizing using a known mold clamping machine, and keeping the pressurized mold at the above temperature by internal heating or external heating to form a preform. Can be. This pressing is at least 10
Minutes, preferably about 30 minutes to 3 hours.

When a preform is prepared at or near room temperature in the presence of moisture, the preform is heated to 80 ° C.
It is preferable to heat and bake at 300 to 600 ° C. after heating and drying before and after.

The above-mentioned ceramic raw material composition used in the present invention, unlike the raw material composition used in the conventional method, can be formed into a tough ceramic molded product even when fired at a relatively low temperature. For example, the temperature is gradually increased from about 100 ° C., and the final temperature is maintained at 300 to 600 ° C., preferably 350 to 550 ° C., for 0.5 to 30 hours, thereby forming ceramics, thereby producing a good ceramic molded product.

The firing atmosphere may be air or an inert gas. Thus, the preform made of the above ceramic raw material composition becomes a ceramic molded product having good heat resistance even at such relatively low temperature forming / firing.

However, when the firing temperature exceeds 600 ° C., it becomes difficult to dissolve and remove the water-soluble halide from the fired ceramic molded product in the elution step described below, and the porous molded product intended in the present invention is not used. Cannot be manufactured.

In the method of the present invention, the halide-containing ceramic molded product obtained by firing as described above is further subjected to
By treating with water or an aqueous solution, the water-soluble halide is dissolved and removed (eluted) from the ceramic molded product to make the ceramic molded product porous.

This elution treatment can be performed at room temperature.
By treating the ceramic molded product in warm water at 25 to 100 ° C., it can be more efficiently performed,
Usually, it is carried out by immersing the ceramic molded article in a warm water bath and stirring the liquid.

Thus, the water-soluble halide in the ceramic molded product is eluted to produce a porous ceramic molded product having a low specific gravity.

[0034]

EXAMPLES Next, examples and comparative examples of the method of the present invention will be described, but these are intended to help the understanding of the present invention, and do not limit the scope of the present invention. Unless otherwise noted, "parts" in the examples
Means parts by weight.

[Example 1] Sodium chloride 60 was added to 100 parts of fly ash obtained as coal ash from a thermal power plant.
Part, powdered monobasic aluminum phosphate inorganic binder ("Aluminum monophosphate 100P" manufactured by Taki Chemical Co., Ltd.)
70 parts and 10 parts of alumina powder as a curing regulator were mixed to prepare a homogeneous ceramic raw material composition.

This raw material composition was prepared with an inner size of 125 mm × 15
It was placed in a 0 mm mold and held at a surface pressure of 300 kg / cm ² for 120 minutes by a mold clamping machine heated to 300 ° C. to perform hot press molding (press molding).

After cooling, the panel-shaped ceramic molded product (molded plate) obtained by taking out from the mold has a hard and dense structure, an apparent specific gravity of 1.60 and a bending strength (3).
Point bending) is 248 kg / cm ² , and the flexural modulus is 214 T.
on / cm ² .

Next, this ceramic molded product was
The molded product was immersed in a warm water bath at a temperature of 5 ° C. for 5 hours with stirring to elute sodium chloride in the molded product, and then dried by heating. As a result, a porous ceramic molded product (molded plate) having an apparent specific gravity of 1.20 was obtained. This decrease in apparent specific gravity corresponded to the amount of sodium chloride added to the raw material composition.

The resulting porous ceramic molded article had a flexural strength of 53 Kg / cm ² and a flexural modulus of 62 Ton / c.
m ² . When the cross section of this porous ceramics molded article was observed with an electron microscope, microscopic cubic cavities corresponding to the crystals of sodium chloride were observed, confirming that the porous ceramics had a porous structure.

Example 2 The same fly ash as in Example 1 was mixed with 100 parts of fly ash, 60 parts of sodium bromide, and a powdered monobasic aluminum phosphate-based binder (“Aluminum monophosphate 100P” manufactured by Taki Kagaku Co., Ltd.). ") 70 parts and 10 parts of alumina powder as a curing regulator were mixed homogeneously, and the obtained raw material composition was placed in a mold having the same size as that of Example 1;
Using a mold clamper heated to 0 ° C, surface pressure 50Kg / cm
² was held for 90 minutes to perform hot pressing. afterwards,
Heating at 300 ° C. was continued for 120 minutes, and after cooling, the product was taken out of the mold to obtain a panel-shaped ceramic molded product. The apparent specific gravity of this molded product was 1.67.

This molded product was subjected to hot water immersion in the same manner as in Example 1 to obtain a porous ceramic molded product (molded plate) having an apparent specific gravity of 1.24. The flexural strength of this porous molded product was 81 kg / cm ² , and the flexural modulus was 69 Ton /
cm ² .

Example 3 In 100 parts of fly ash as in Example 1, 50 parts of sodium chloride and a powdered aluminum phosphate monobasic binder ("Aluminum monophosphate 100P" manufactured by Taki Kagaku Co., Ltd.) 30), 10 parts of alumina powder as a curing regulator and 21 parts of water (corresponding to 10% by weight with respect to the total composition) were mixed to obtain a homogeneous ceramic raw material composition.

This raw material composition was placed in a mold similar to that in Example 1, press-molded at room temperature at 30 kg / cm ^{2 at a} surface pressure for 15 minutes, taken out of the mold, and heated at 80 ° C. for 1 minute.
After pre-drying for 20 minutes, 100-300 ° C in an electric furnace
The temperature was raised to 0 ° C. and heated to fire. The apparent specific gravity of the obtained ceramic molded product was 1.39.

The molded product was immersed in a warm water bath at 70 ° C. to elute sodium chloride in the molded product, and then dried to obtain a molded product having an apparent specific gravity of 1.03. Confirmed that Moreover, the bending properties of the porous ceramic molded article was measured, the flexural strength 20 Kg / cm ^2, a flexural modulus of 27Ton / cm ^2.

Example 4 100 parts of fly ash as in Example 1, 50 parts of sodium chloride, and a powdered monobasic aluminum phosphate-based binder as an inorganic binder ("Taki Kagaku Co., Ltd." Aluminum monophosphate 100P ") 1.
5 parts of a liquid monobasic aluminum phosphate-based binder (57.0 parts of "Acidophos 120M" manufactured by Taki Kagaku Co., Ltd. [including 28.5 parts of water]) and 10 parts of hydrated alumina as a curing regulator Thus, a homogeneous ceramic raw material composition was prepared.

This raw material composition was placed in a mold having the same size as in Example 1, and at room temperature, 50 kg / cm ^{2 and a} surface pressure of 15 kg.
After press-molding for minutes, it was taken out of the mold, pre-dried, and fired at 300 ° C. The apparent specific gravity of the obtained ceramic molded product was 1.44.

The molded product was immersed in a warm water bath at 70 ° C. to elute sodium chloride in the molded product, and then dried to obtain a molded product having an apparent specific gravity of 1.07. Confirmed that.

The flexural strength of this porous ceramic molded product was 17 kg / cm ² and the flexural modulus was 17 Ton / cm ^2.
Met.

Example 5 100 parts of fly ash as in Example 1, 50 parts of sodium chloride, 50 parts of powdery sodium silicate crystal (anhydride) as an inorganic binder, 10 parts of alumina as a curing regulator and water 23.3 parts (corresponding to 10% by weight of the total composition) were mixed to prepare a homogeneous ceramic raw material composition.

This raw material composition was placed in a mold having the same size as in Example 1, and was heated to 100 ° C. using a mold clamping machine.
After press molding at a surface pressure of 50 kg / cm ² for 60 minutes, the molded product was taken out of the mold and fired in an electric furnace at 500 ° C. to obtain a ceramic molded product having an apparent specific gravity of 1.35.

The molded product is immersed in a warm water bath at 60 to 70 ° C. to elute sodium chloride in the molded product, and the molded product obtained by drying has an apparent specific gravity of 0.95 and is porous. Has been confirmed.

The flexural strength of this porous ceramic molded product was 103 kg / cm ² , and the flexural modulus was 60 Ton / cm.
² showed good physical properties.

Example 6 To 100 parts of fly ash as in Example 1, 50 parts of sodium chloride, 50 parts of sodium silicate (anhydride) and 36.3 parts of water (1 part in the total composition)
(Equivalent to 5.4% by weight) to prepare a homogeneous ceramic raw material composition.

This raw material composition was placed in the same mold as in Example 1, press-molded at room temperature at a surface pressure of 50 Kg / cm ² for 60 minutes, and then calcined at 500 ° C. to give an apparent specific gravity of 1. Forty-five ceramic moldings were obtained.

This molded product is immersed in a warm water bath at 70 ° C. to elute sodium chloride in the molded product, and the molded product obtained by drying has an apparent specific gravity of 1.02 and is porous. It was confirmed that.

The flexural strength of this porous ceramic molded product was 137 kg / cm ² , and the flexural modulus was 81 Ton / cm.
² showed good physical properties.

Example 7 100 parts of fly ash as in Example 1 were mixed with 60 parts of sodium chloride and a powdered monobasic aluminum phosphate-based binder (“Aluminum monophosphate 100P” manufactured by Taki Kagaku Co., Ltd.) A homogeneous ceramic raw material composition was prepared by mixing 30 parts of a liquid monobasic aluminum phosphate-based binder (50 parts of "Acidophosis 100L" manufactured by Taki Kagaku Co., Ltd.) and 5 parts of zinc chloride as a curing regulator. .

This raw material composition was placed in the same mold as in Example 1 and press-molded at room temperature at a surface pressure of 30 kg / cm ² for 30 minutes. Next, after pre-drying was performed in a constant temperature bath at 80 ° C., it was transferred to an electric furnace and baked while raising the temperature from 100 ° C. to 400 ° C. The apparent specific gravity of the obtained ceramic molded product was 1.71.

This molded product was immersed in a hot water bath at 70 ° C. to elute sodium chloride in the molded product, and dried to obtain a porous ceramic molded product having an apparent specific gravity of 1.27. The bending strength of this porous ceramic molded product is 127 kg / cm ² , and the flexural modulus is 113 Ton / cm.
² showed good physical properties.

[0060]

As described above, according to the method of the present invention, a heat-resistant ceramic molded article having excellent porosity and light weight can be manufactured. In particular, even when the sintering temperature is relatively low as described above, a heat-resistant porous ceramic molded article that can withstand 1000 ° C. can be produced.

Since this molded article has a substantially uniform porous structure, it not only has excellent lightness, but also has heat insulation, soundproofing, air permeability, and water retention. It can be used effectively.

Accordingly, the ceramic molded article according to the method of the present invention can be effectively used in a wide range of applications, for example, in the construction field such as structural materials for buildings, finishing materials and decorative materials, soundproof side walls of roads and underwater floating bodies. Can be.

Claims (9)

[Claims] 1. A ceramic raw material composition is prepared by mixing coal ash, an inorganic binder and at least one of a water-soluble alkali metal or alkaline earth metal halide, and then using a mold to form the ceramic raw material composition. An article is formed into a predetermined shape and fired at a temperature of 300 to 600 ° C. to form a ceramic article, and then the water-soluble halide is dissolved and removed from the article with water or an aqueous solution to form the article. A method for producing a porous ceramics molded article, comprising: 2. A ceramic raw material composition is prepared by mixing coal ash, an inorganic binder, at least one water-soluble alkali metal or alkaline earth metal halide, and a hardening modifier, and then forming a mold. After shaping the composition into a predetermined shape by using it and baking it at a temperature of 300 to 600 ° C. to form a ceramic molded product, the water-soluble halide is dissolved and removed from the molded product with water or an aqueous solution. A method for producing a porous ceramics molded article, wherein the molded article is made porous. 3. A composition comprising coal ash, an inorganic binding agent and a water-soluble alkali metal or alkaline earth metal halide, or a ceramic raw material composition further comprising a hardening modifier added thereto, wherein coal ash is added. The method for producing a porous ceramic molded product according to claim 1 or 2, wherein the molding is performed in a state in which water is added in an amount of 40 parts by weight or less per 100 parts by weight. 4. The inorganic binder according to claim 1, wherein the first binder is an aluminum phosphate powder, an aqueous solution mainly containing aluminum phosphate, or an aqueous solution mainly containing sodium silicate or sodium silicate. 4. A method for producing a porous ceramic molded product according to claim 3. 5. An alkali metal or alkaline earth metal halide having an average particle size of 0.0
The method for producing a porous ceramic molded product according to any one of claims 1 to 4, wherein the porous ceramic molded product is a powder or a crystal having a shape of 1 to 1 mm. 6. The production of a porous ceramic molded product according to claim 1, wherein the alkali metal or alkaline earth metal halide is sodium chloride or potassium bromide. Method. 7. The curing control agent according to claim 1, wherein the curing regulator is at least one selected from aluminum, zinc, magnesium and calcium.
The method for producing a porous ceramic molded product according to any one of claims 1 to 6, wherein the metal oxide is a metal oxide or hydroxide. 8. The blending ratio of coal ash / inorganic binder / alkali metal or alkaline earth metal halide is 10 to 150 parts by weight of inorganic binder, 100 parts by weight of coal ash, alkali metal or alkali. 2. The method according to claim 1, wherein the amount of the earth metal halide is 5 to 100 parts by weight.
A method for producing a porous ceramic molded product according to any one of claims 1 to 7. 9. The porous ceramic molding according to claim 2, wherein the amount of the curing regulator is 1 to 20 parts by weight based on 100 parts by weight of coal ash. Method of manufacturing a product.