JP2010095444A - Solidification method of ceramics - Google Patents

Abstract

Disclosed is a method for solidifying ceramic powder, which does not require high-temperature firing and provides a solidified ceramic body having excellent mechanical strength.
An activated ceramic powder whose surface is mechanochemically amorphized is obtained by grinding ceramics having at least a surface made of silicic acid and / or silicate. The activated ceramic powder thus obtained is treated with an alkaline aqueous solution containing an alkali metal hydroxide and / or an alkaline earth metal hydroxide, so that the surface of the activated ceramic powder is dissolved and re-precipitated. A solidified body is obtained.
[Selection] Figure 1

Description

  The present invention relates to a method of solidifying ceramic powder without using high-temperature sintering without using a binder such as cement or water glass.

  Since cement clinker is baked by mixing limestone with clay, there are carbon dioxide emission by burning limestone and carbon dioxide emission by burning heavy oil fuel. For this reason, it is said that 1 ton of carbon dioxide is generated to burn 1 ton of cement clinker. In recent years, global warming has become a global problem, and the regulation of carbon dioxide emission has become an important issue. Therefore, development of a new alternative technology to replace cement is required.

  Under such circumstances, as an energy-saving material that does not depend on limestone and does not need to be fired, a room temperature solidified ceramic solidified body in which ceramic powder is bound using water glass as a binder has attracted attention (for example, (See Patent Documents 1 to 4). In this ceramic solidified 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. Then, dehydration condensation occurs as the water evaporates, resulting in a solidified ceramic.

  As described above, according to the ceramic solidified body that solidifies the filler using water glass, a building material such as a block can be easily obtained without using limestone (for 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.

JP-A-8-301638 JP-A-8-301039 JP 7-133147 A JP 2003-22669 A

  However, in the ceramic solidified body using the conventional water glass as a binder, the solubility of the ceramic varies greatly 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 solidified ceramic body with high 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.

  The present invention has been made in view of the above-described conventional circumstances, and solves the problem of providing a method for solidifying ceramic powder that does not require high-temperature firing and that can provide a solidified ceramic body having excellent mechanical strength. It is an issue that should be done.

  The inventors considered not using water glass as a conventional binder, but using a mechanochemical phenomenon to obtain a solidified ceramic body. 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 reacted, melt | dissolved and reprecipitation occurred, it discovered that it solidified, and came to complete this invention.

That is, the method for solidifying the ceramic powder of the present invention comprises:
A step of forming an amorphous part on the surface of the semi-lux powder by a mechanochemical action;
In the liquid in which the amorphous part can be dissolved, the amorphous part is dissolved and reprecipitated to form a precipitated layer, and the ceramic powder is mainly solidified by the precipitated layer;
The first feature is to include

  In addition, a semi-lux powder with an amorphous part formed on the surface by mechanochemical action is prepared, and the amorphous part of the semi-lux powder is dissolved and reprecipitated in a solution in which the amorphous part can be dissolved. The second feature is to form a precipitation layer and solidify the ceramic powders mainly by the precipitation layer.

  The third feature is that the ceramic powders are solidified only by the deposited layer.

  Since the ceramic solid body thus obtained does not use water glass, the shrinkage due to dehydration is not so large, and there are few distortions and voids, and the mechanical strength is also high. 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.

  Therefore, according to the method for solidifying ceramic powder of the present invention, high-temperature firing is unnecessary, and a ceramic solidified body having excellent mechanical strength can be obtained.

It is a schematic diagram which shows the solidification principle in the manufacturing method of the ceramic solidification body of this invention. It is a graph which shows the relationship between ball mill time and the intensity | strength of a ceramic solidification body.

<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 solidified 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.

  Moreover, as ceramics which only the surface consists of silicic acid and / or silicate, for example, silicon nitride, silicon carbide, aluminosilicate (zeolite), sialon (SiAlON), silicon oxynitride (SiON), silicon oxycarbide ( SiOC) and the like.

Aggregates can also be used in combination. Such aggregates include sand, crushed sand, gravel, crushed stone, quartz sand, quartzite powder, crystalline alumina, fly ash, alumina, mica, diatomaceous earth, mica, rock powder (shirasu, anti-fluorite, etc.), basalt, feldspar, Wollastonite, clay, bauxite, sepiolite, fiber material, etc. 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.
<Alkali treatment process>
In the alkali treatment step, the activated ceramic powder 2 is treated with an alkaline aqueous solution containing an alkali metal hydroxide and / or an alkaline earth metal hydroxide. Examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. Examples of the alkaline earth metal hydroxide include calcium hydroxide and barium hydroxide.

  The apparatus for mixing and kneading the alkaline aqueous solution and the activated ceramic powder 2 is not particularly limited, and any conventionally known mixer or kneader can be used. Examples thereof include a double-arm kneader, a pressure kneader, an Eirich mixer, a super mixer, a planetary mixer, a Banbury mixer, a continuous mixer, and a continuous kneader. It is also preferable to use a vacuum kneader to remove bubbles. This can prevent bubbles from remaining in the solidified ceramic body.

  By this treatment, 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 to obtain a solidified ceramic body 3. In this alkali treatment step, the dissolution reaction of the amorphous layer 2a and the dehydration condensation reaction 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.

  By the way, in the ceramic solidified body using the conventional water glass described in the background art column 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 solidified ceramic body with high 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.

  On the other hand, since the ceramic solidified body obtained by the method described in the column of the embodiment of the invention does not use water glass, a shrinkage ratio due to dehydration is not so large, and a molded body excellent in dimensional accuracy is manufactured. can do. Moreover, there are few distortions and voids, the mechanical strength is increased, and the strength of the obtained ceramic solidified body can be 10 MPa or more.

  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 solidification method of the ceramic powder described in the embodiment of the invention, high-temperature firing is unnecessary, the solidification control is easy, the mechanical strength and the dimensional accuracy are excellent, and the appearance is also good. Well, it consumes less energy during production and can use a wide range of resources.

Hereinafter, examples embodying the present invention will be described in detail. Example 1
In Example 1, a ceramic solidified body was manufactured through the following steps using metakaolin (average particle diameter: 1 μm) obtained by baking and dehydrating kaolinite and using an aqueous potassium hydroxide solution as an alkaline aqueous solution. <Milling process>
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. <Alkali treatment process>
The activated metakaolin powder obtained by the milling process is added with a 50% by weight potassium hydroxide solution to the raw material by 65% by weight, extruded using a vacuum kneader, cut into a predetermined length, and prismatic. A mixture of was obtained. Furthermore, this mixture was put into a dryer set at 40 ° C. and heat-dried for 24 hours to obtain the solid metakaolin 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 the description is 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 the description is 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. 2, in the ceramic solidified bodies of Examples 1 to 5, 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.

  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.

  INDUSTRIAL APPLICABILITY The present invention is an energy saving type and can be used in many industrial fields as a structural material that emits less carbon dioxide during production.

DESCRIPTION OF SYMBOLS 1 ... Ceramics 2 ... Activated ceramic powder 2
2a ... amorphous layer 3 ... solidified ceramic 3a ... deposited layer

Claims (3)

A step of forming an amorphous part on the surface of the semi-lux powder by a mechanochemical action;
In the liquid in which the amorphous part can be dissolved, the amorphous part is dissolved and reprecipitated to form a precipitated layer, and the ceramic powder is mainly solidified by the precipitated layer;
A method of solidifying ceramic powder, comprising:   A semi-lux powder having an amorphous part formed on the surface by a mechanochemical action is prepared, and the amorphous part of the semi-lux powder is dissolved in a solution in which the amorphous part can be dissolved. A method for solidifying a ceramic powder, characterized in that the ceramic powder is solidified mainly by the deposited layer by forming a deposited layer.   3. The method for solidifying ceramic powder according to claim 1, wherein the ceramic powder is solidified only by the deposited layer.