JP5061348B2 - Ceramic porous body manufacturing method and ceramic porous body - Google Patents

Description

  The present invention relates to a method for producing a ceramic porous body without using ceramic or powdery binders such as cement and water glass and without high-temperature sintering, and a ceramic porous body produced by the method.

  In recent years, global warming has become a global problem, and regulation of carbon dioxide emission has become an important issue. Under such circumstances, as a new alternative technique to replace cement, a room temperature solidified ceramic porous body in which ceramic powder is bonded using water glass as a binder is attracting attention (for example, Patent Documents 1 to 4). In this ceramic porous body, water glass and a filler such as metakaolin are mixed, and metal ions such as aluminum are eluted from the filler and reacted with water glass. Thereby, sodium silicate which is a component of water glass is crosslinked to become an inorganic polymer. And dehydration-condensation occurs with the evaporation of moisture, resulting in a porous ceramic body.

  As described above, according to the ceramic porous body that solidifies the filler using water glass, a building material such as a block can be easily obtained at room temperature without using limestone (for the activation of the filler). It is desirable to fire at about 750 ° C., but still much lower than the firing temperature of cement clinker). For this reason, the amount of carbon dioxide generated during production is much less than that of cement.

Furthermore, when solidifying the filler using water glass, a ceramic porous body is also known by mixing a foaming agent and solidifying the foamed state (Patent Document 5). The ceramic porous body thus obtained is lightweight and has excellent heat insulation properties.
JP-A-8-301638 JP-A-8-301039 JP 7-133147 A JP 2003-22669 A JP 2000-313678 A

  However, in the ceramic porous body using the conventional water glass as a binder, the solubility of the ceramic greatly varies depending on the ratio of silicon and sodium in the water glass and the degree of polymerization. For this reason, it is difficult to control solidification, and it is difficult to obtain a ceramic porous body having high strength with good reproducibility. In addition, since a large amount of water glass is used, the water in the water glass evaporates, and is apt to be distorted or cracked, resulting in inferior mechanical strength. Moreover, since shrinkage occurs due to evaporation of moisture, there is a problem that the dimensional accuracy is inferior. Furthermore, since a large amount of water glass is used, there is a problem that the water glass component is raised on the surface and becomes white and dirty. Moreover, since it is necessary to mix water glass and ceramic powder with high viscosity well, there was a problem that much energy and time were required for mixing. Furthermore, in order to cause a large amount of water glass and ceramics to chemically react, it is necessary that the ceramics have a silicic acid or silicate phase not only on the surface but also to some extent inside.

  The present invention has been made in view of the above-described conventional circumstances, does not require high-temperature firing, is easy to control solidification, has excellent mechanical strength and dimensional accuracy, has a good appearance, and is manufactured. It is an issue to be solved to provide a method for producing a ceramic porous body that consumes a small amount of energy and can use a wide range of resources as a raw material, and a ceramic porous body.

  The inventors have considered to obtain a ceramic porous body by utilizing a mechanochemical phenomenon, instead of using water glass as a conventional binder. The mechanochemical phenomenon is a change in chemical bond or electron density distribution in a solid that has been subjected to impact stress or shear stress due to crushing, etc., causing various chemical reactions due to charge transfer locally or thermal processes. This is a phenomenon in which excitation of electron energy occurs, unlike the excited state at. Silicic acid and silicate can be made amorphous by mechanochemical treatment. For this reason, if this phenomenon is utilized and the powder of silicic acid or silicate is ground by a ball mill or the like to make it amorphous, and further an alkali acts, the amorphous phase and the alkali are separated. It was found that the solution reacted and dissolved and reprecipitated to solidify. Furthermore, it was found that a ceramic porous body can be obtained by adding a foaming agent together with an alkali and solidifying in a foamed state, thereby completing the present invention.

That is, the method for producing a ceramic porous body of the present invention includes:
A grinding step to obtain an activated ceramic powder whose surface is mechanochemically amorphized by grinding ceramic comprising at least the surface of silicic acid and / or silicate;
An alkaline aqueous solution containing an alkali metal hydroxide and / or alkaline earth metal hydroxide and a foaming agent are added to the activated ceramic powder, and the surface of the activated ceramic powder is left in a foamed state. A porous body forming step for obtaining a ceramic porous body by dissolution and reprecipitation; and
It is characterized by providing.

The ceramic powder used as a raw material has at least a surface made of silicic acid and / or silicate, so that the surface is mechanochemically amorphized by the grinding process and activated ceramic powder in a state susceptible to alkali attack. Become a body. In the porous body forming step, the amorphous phase present on the surface of the activated ceramic powder is invaded and dissolved by the alkali under the state of being foamed by the action of the foaming agent, and further the dehydration condensation reaction occurs. It re-deposits and solidifies while leaving bubbles. In this way, a ceramic porous body is manufactured.
Also, an activated ceramic powder having at least a surface made of silicic acid and / or silicate made mechanochemically amorphous is prepared, and the activated ceramic powder is alkali metal hydroxide. It is also possible to obtain a porous ceramic body by adding an aqueous solution of a product and / or an alkaline earth metal hydroxide and a foaming agent and solidifying the foamed state.

Since the ceramic porous body thus obtained does not use water glass, the shrinkage rate due to dehydration is not so large, and a ceramic porous body excellent in dimensional accuracy can be manufactured. Moreover, there is little distortion and mechanical strength is also increased.
Further, since water glass whose properties vary greatly depending on the degree of polymerization or the like is not used, control is easy and quality stability such as mechanical strength is excellent.
Furthermore, unlike water glass, which is highly viscous and difficult to uniformly mix with raw materials, alkaline aqueous solutions containing alkali metal hydroxides and / or alkaline earth metal hydroxides have low viscosity and Uniform mixing is easy, energy required for mixing is small, and mixing time is short. Moreover, since uniform mixing becomes easy, the problem that the appearance is stained white due to segregation of alkali hardly occurs.

  Therefore, according to the method for producing a porous ceramic body of the present invention, high-temperature firing is not required, solidification control is easy, mechanical strength and dimensional accuracy are excellent, good appearance, and energy during production. Can consume a wide range of resources.

  Examples of the alkali metal hydroxide contained in the alkaline aqueous solution in the porous body forming step include potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. In addition, calcium hydroxide, barium hydroxide, or the like is used as the alkaline earth metal hydroxide contained in the alkaline aqueous solution in the porous body forming step.

Moreover, when obtaining a ceramic porous body, it can be set as a foamed state by rotating the stirring blade of a porous body stirrer and stirring while entraining air. Moreover, it can be set as the foamed state by stirring while sending air from the downward direction. Further, a surfactant can be used as a foaming agent, and the surfactant solution can be added in a previously foamed state. Moreover, the substance which reacts with alkaline aqueous solution and generate | occur | produces hydrogen as a foaming agent can be made into the state bubbled with the generated hydrogen.
The strength of the ceramic porous body obtained by the method for producing a ceramic porous body of the present invention can be 7 MPa or more.

The ceramic porous body of the present invention can be obtained by the method for producing a ceramic porous body of the present invention. That is, the ceramic porous body of the present invention comprises an alkali metal hydroxide and an activated ceramic powder obtained by mechanochemically amorphizing at least a surface of a ceramic made of silicic acid and / or silicate. / or an aqueous solution of an alkaline earth metal hydroxide, which has been added a foaming agent to solidify the whipped state,
The ceramic powder is solidified through a deposited layer formed by dissolving and reprecipitating the amorphous portion .

<Raw materials>
The ceramics used as a raw material are required to have at least a surface made of silicic acid and / or silicate. Examples of such ceramics include clay minerals such as bentonite, kaolinite, metakaolin, and montmorillonite, and SiO ₂ —Al ₂ O ₃ inorganic powders such as quartz and mullite. Among these, clay minerals and quartz are preferable because they are inexpensive and can be obtained in large quantities. The inventors have obtained a porous ceramic body that is dense and excellent in mechanical strength when metakaolin is used as a clay mineral.
In addition, waste such as fly ash, glitter, glass, paper sludge, and aluminum dross can be used as ceramics.
Examples of ceramics whose surface is made of silicic acid and / or silicate include silicon nitride, silicon carbide, sialon (SiAlON), silicon oxynitride (SiON), silicon oxycarbide (SiOC) and the like. .

Moreover, the aggregate which at least the surface consists of silicic acid and / or silicate can also be used together. Such aggregates include sand, crushed sand, gravel, crushed stone, quartz sand, quartzite powder, fly ash, mica, diatomaceous earth, mica, rock powder (such as shirasu, anti-fluorite), basalt, feldspar, wollastonite, clay, bauxite Sepiolite, a fiber material having at least a surface made of silicic acid and / or silicate, or the like can be used.

<Milling process>
In the grinding step, as shown in FIG. 1, an amorphous layer whose surface is mechanochemically amorphized by grinding ceramics 1 having at least a surface made of silicic acid and / or silicate. The activated ceramic powder 2 having 2a is obtained. In the amorphous layer 2a, the network structure of silica is in an amorphous state, and is easily eroded by alkali.
In order to perform such a mechanochemical action, it is effective to apply various forces such as impact, friction, compression, and shearing in a composite manner. Examples of the apparatus capable of performing such an action include a mixing apparatus such as a ball mill, a vibration mill, a planetary mill, and a medium stirring mill, a ball medium mill, a roller mill, a pulverizer such as a mortar, and the like. Is not to be done. Further, a jet crusher or the like that can mainly apply a force such as impact and grinding to the object to be crushed can also be used. If it is pulverized with a jet pulverizer, compressive force, shear force, impact force, etc. can be applied, thereby silicic acid and / or silicate on the ceramic surface is made amorphous and activated ceramic powder. Can do.

  In the grinding step, it is preferable to grind until there is no change with time in the particle size distribution. Grinding until there is no change over time in the particle size distribution is considered to have reached the limit that the ceramic 1 can be made fine by grinding, and the mechanochemical amorphization of the ceramic surface is the most advanced state. ing. The activated ceramic powder 2 obtained by grinding to such a state is likely to proceed with dissolution with an alkaline aqueous solution, and the obtained ceramic solidified body becomes dense and has high mechanical strength.

<Porous body forming step>
In the porous body forming step, an alkaline aqueous solution containing an alkali metal hydroxide and / or an alkaline earth metal hydroxide and a foaming agent are added to the activated ceramic powder 2, and a stirring blade is moved at high speed by a stirrer. Rotate to stir while entraining air, or send air from below and stir to mix while generating bubbles 2b.

  Then, due to the action of the added alkali, the amorphous layer 2a on the surface of the activated ceramic powder 2 is dissolved and further dehydrated and condensed to form a deposited layer 3a. The deposited layer 3a serves as an adhesive, and a ceramic porous body 3 having a large number of holes 3b due to the bubbles 2b is obtained. In this porous body forming step, the dissolution reaction and dehydration condensation reaction of the amorphous layer 2a may be performed at room temperature, or can be accelerated by heating. The reaction temperature may be appropriately selected depending on the type of ceramic as a raw material and the type and concentration of the aqueous alkali solution, but generally room temperature to 200 ° C. is preferable, and room temperature to 60 ° C. is more preferable.

As the foaming agent, various surfactants such as alkylbenzene sulfonate, polyoxyethylene ether, natural resin, polyether alkylbenzene sulfonate, and higher alkyl ether sulfate can be used. Specific examples include sodium dialkylsulfosuccinate, ammonium lauryl sulfate, dodecylbenzenesulfonic acid, polyoxyethylene sorbitan monolaurate, polyoxyethylene monooleate, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, and the like.
Moreover, when adding these surfactant solutions, you may make it add a surfactant solution in the state bubbled beforehand. If it is like this, the state of a bubble can be stabilized more.
Further, as a foaming agent, a substance that reacts with an alkali such as aluminum powder, zinc powder, and Si simple substance powder to generate hydrogen can be mixed and foamed with hydrogen bubbles. Moreover, when using an aggregate together, it is also possible to set it as the aggregate containing the substance which generate | occur | produces hydrogen by reacting with an alkali.

Hereinafter, examples embodying the present invention will be described in detail.
Example 1
In Example 1, a solidified ceramic body was manufactured through the process shown in FIG. 2 using metakaolin (average particle size: 1 μm) obtained by baking and dehydrating kaolinite and using an aqueous potassium hydroxide solution as an alkaline aqueous solution. Details are as follows.

<Milling step (S1)>
200 g of the metakaolin was put into a 1000 mL magnetic pot, zirconia balls (diameter: 10φ) were charged, and rotated for 100 hours with a ball mill device to obtain activated metakaolin powder.

<Porous body forming step (S2)>
The activated metakaolin powder obtained by the milling process is mixed with a 50% by weight potassium hydroxide solution added to the raw material by 65% by weight, and defoamed with a vacuum device to remove bubbles present in the slurry. Remove. To 100 g of this mixture, an 80% aqueous solution of sodium dialkylsulfosuccinate as a foaming agent was added at a rate of 6 ml, and the stirring blade of the stirrer was immersed in the mixture and rotated at high speed for 3 minutes to cause foaming. A slurry having Then, this slurry was poured into a mold, put into a drier set at 40 ° C., and heat-dried for 24 hours to obtain a metakaolin porous body of Example 1.

(Examples 2 to 5)
In Example 2, the rotation time of the pot in the grinding process was 70 hours, Example 3 was 50 hours, Example 4 was 25 hours, and Example 5 was 10 hours. Other conditions are the same as those in the first embodiment, and a description thereof will be omitted.

(Comparative Example 1)
In Comparative Example 1, the grinding step was not performed. Other conditions are the same as those in the first embodiment, and a description thereof will be omitted.

<Evaluation>
With respect to the solidified ceramic bodies of Examples 1 to 5, the three-point bending strength was measured at room temperature using a strength test apparatus in accordance with JIS R 1601. As a result, as shown in FIG. 3, it was found that the strength of the metakaolin solidified body increases as the ball mill time increases. From this, by increasing the ball mill time, the amorphization of the surface of the metakaolin particles proceeds, and in the alkaline treatment step, the amorphized surface is eluted and re-precipitated by potassium hydroxide. It turned out to be a solid metakaolin solidified body.
On the other hand, in Comparative Example 1, it could not be solidified and measurement was impossible.

(Examples 6 to 8)
In Example 6, 85% by mass of a 50% by mass potassium hydroxide solution was added to the activated metakaolin powder. Other conditions are the same as those in the fourth embodiment, and a description thereof will be omitted.
Moreover, Example 7 is the same as Example 4 except that ammonium lauryl sulfate was used as the foaming agent, and a description thereof will be omitted.
Furthermore, in Example 8, 85% by mass of a 50% by mass potassium hydroxide solution was added to the activated metakaolin powder. The other conditions are the same as in Example 7, and the description is omitted.

Examples 6-8 The porosity and strength were measured for the metakaolin porous material. As a result, as shown in Table 1, high strength that can be practically used sufficiently was obtained. Moreover, it turned out that the porosity of Example 4 and 7 with few mixing ratios of potassium hydroxide solution becomes high compared with Example 6 and 8 with many mixing ratios. This is considered to be because when the added amount of the aqueous potassium hydroxide solution is small, the viscosity increases and bubbles are difficult to escape. Further, by utilizing this fact, the porosity can be controlled by adjusting the amount of potassium hydroxide aqueous solution added.

  The present invention is not limited to the description of the embodiments of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

It is a schematic diagram which shows the manufacturing method of the ceramic porous body of this invention. It is process drawing of the ceramic porous body manufacture in Examples 1-8. It is a graph which shows the relationship between the ball mill time in Examples 1-5, and the intensity | strength of a ceramic porous body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ceramics 2 ... Activated ceramic powder 2a ... Amorphous layer 2b ... Bubble 3 ... Ceramic porous body 3a ... Precipitation layer 3b ... Hole S1 ... Grinding process S2 ... Porous body formation process

Claims (7)

A grinding step to obtain an activated ceramic powder whose surface is mechanochemically amorphized by dry grinding a ceramic comprising at least a surface of silicic acid and / or silicate;
An alkaline aqueous solution containing an alkali metal hydroxide and / or alkaline earth metal hydroxide and a foaming agent are added to the activated ceramic powder, and the surface of the activated ceramic powder is left in a foamed state. A porous body forming step of obtaining a ceramic porous body having a strength of 7 MPa or more by dissolving and reprecipitation;
A method for producing a ceramic porous body, comprising:   2. The method for producing a ceramic porous body according to claim 1, wherein the ceramic as a raw material contains clay mineral and / or quartz as main components. The method for producing a ceramic porous body according to claim 2 , wherein the clay mineral is metakaolin. The method for producing a ceramic porous body according to any one of claims 1 to 3 , wherein the foamed state is obtained by rotating the stirring blade of the stirrer and stirring while entraining air. The method for producing a ceramic porous body according to any one of claims 1 to 3 , wherein the foamed state is obtained by stirring while feeding air from below. The method for producing a ceramic porous body according to any one of claims 1 to 3 , wherein a surfactant is used as the foaming agent, and the surfactant solution is added in a previously foamed state. The porous ceramic body according to any one of claims 1 to 3 , wherein a substance that generates hydrogen by reacting with an alkaline aqueous solution is used as the foaming agent, and the foamed state is caused by the generated hydrogen. Production method.

Images