JP2018123027A - Silica/graphite-based uncalcinated solidified body, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silica/graphite-based uncalcinated solidified body which is excellent in mechanical strength and has high electric conductivity; and to provide a method for producing the same.SOLUTION: An activated silica has: inner core particles which consist of silica; and an activation layer which forms a shell of the inner core particles and is activated mechanochemically. In a silica/graphite-based uncalcinated solidified body of this invention, the activation layers of the activated silica are bonded together through dehydration condensation to form the solidified body, and graphite particles are included in the activation layer bonded through the dehydration condensation and are distributed. The silica/graphite-based uncalcinated solidified body can be produced by: grinding silica in a dried state to form the activation layer on a surface of the silica particles as the activated silica (an activation step S11); adding the graphite to the activated silica and then mixing them (a mixing step S12); and adding a potassium hydroxide solution to dissolving and reprecipitating the activation layer (a solidifying step S13).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a silica / graphite non-fired solidified body in which silica and graphite are combined and solidified without firing, and a method for producing the same.

  In the manufacture of ceramic products such as pottery, cement, and glass, a firing process is essential, and thus a large amount of energy such as heavy oil, gas, and electricity is consumed. In order to solve this problem, the present inventor has developed an unfired solidified body using a mechanochemical reaction that does not require a firing step (for example, Patent Documents 1 to 4).

  In these methods for producing a non-fired solidified body, first, a powder of silicic acid or a silicate compound is ground to form an activated layer mechanochemically. Then, the activated layer is dissolved by hydrolysis with an alkali, and further re-deposited by dehydration condensation, whereby the powders are combined to form a solid. The method for producing a non-fired solidified body using this mechanochemical reaction is easy to control solidification, has excellent mechanical strength and dimensional accuracy, has a good appearance, and can use a wide range of resources as raw materials. Has attracted attention as a method of solidifying ceramic powder

JP 2009-203101 A JP 2009-203102 A JP 2008-239433 A JP 2008-239434 A

  If further improvement in mechanical strength and new functionality can be imparted to the non-fired solidified body using the conventional mechanochemical reaction, it will lead to expansion of new uses of the non-fired solidified body. The present invention has been made in view of such circumstances, and it is an object to be solved to provide a silica / graphite non-fired solidified body having excellent mechanical strength and high electrical conductivity, and a method for producing the same. .

  As a result of diligent research to solve the above problems, the inventors of the present invention made a silica / graphite unfired solidified body obtained by solidifying a mixture of silica and graphite activated by mechanochemical treatment by alkali treatment, It has been found that graphite particles are encapsulated and dispersed in an activated layer bonded by dehydration condensation. And furthermore, it discovered that this solidified body showed the outstanding mechanical strength and high electrical conductivity, and came to complete this invention.

That is, the silica / graphite non-fired solidified body of the present invention is
An activated silica having inner core particles made of silica and an activated layer mechanochemically activated that forms an outer shell of the inner core particles is bonded to each other by dehydration condensation to form a solidified body. ,
The activated layer bonded by the dehydration condensation is characterized in that graphite particles are included and dispersed therein.

  The inner core particles constituting the silica / graphite unfired solidified body of the present invention are made of silica, the activated layer forming the outer shell of the inner core particles is mechanochemically activated, and the activated layers are dehydrated. Bonded by condensation to form a solid. Here, “mechanochemically activated” means that the silica forming the surface of the inner core particle is subjected to impact stress and shear stress by pulverization, etc., and chemical bond and electron density distribution changes, Various chemical reactions due to charge transfer occur locally, or excitation of electron energy occurs unlike the excited state in the thermal process, which means that it is in a chemically active state. Since its active state is not completely clarified, it is impossible or impractical to specifically show the structure, but the siloxane bond of silica is cleaved into radicals. It is said that siloxane bonds are converted to silanol groups by reacting with water. The mechanochemically activated layers are solidified by dehydration condensation. For this reason, it is an unfired solidified body excellent in heat resistance and mechanical strength.

In addition, since the graphite particles are included and dispersed in the activation layer bonded by dehydration condensation, the graphite particles are concentrated on the surface of the three-dimensional network structure formed by the activation layer bonded by dehydration condensation. In other words, there are no graphite particles inside the inner core particles made of silica. For this reason, in the silica / graphite non-fired solidified body of the present invention, the electrical conductivity is effectively enhanced by the graphite particles concentrated on the surface of the three-dimensional network structure formed by the activated layer bonded by dehydration condensation. It will be.
Therefore, the silica / graphite non-fired solidified body of the present invention is excellent in heat resistance and mechanical strength and has high electrical conductivity.

  In the silica / graphite non-fired solidified body of the present invention, the activated layer bonded by dehydration condensation is usually very thin, about 10 nm to 100 nm, and therefore the graphite particles included therein have an extremely small average particle diameter below this. 50 nm or less is also possible.

  Moreover, in the silica / graphite non-fired solidified body of the present invention, graphite particles that are not dispersed may be contained in the activated layer bonded by dehydration condensation. Even in this case, the unfired solidified body of silica / graphite of the present invention has a high mechanical strength due to the three-dimensional network structure formed by the activated layer bonded by dehydration condensation. In addition, the electrical conductivity is effectively increased by the graphite particles concentrated on the three-dimensional network structure.

The silica / graphite unfired solidified body of the present invention can be produced by the following method.
That is, the method for producing the silica / graphite non-fired solidified body of the present invention is as follows:
An activation step in which silica is ground in a dry process to form activated silica in which an activated layer in which the surface of the silica particles is mechanochemically activated is formed;
A mixing step of adding graphite to the activated silica and mixing;
Solidification to obtain a solidified body by dissolving and reprecipitating the activated layer by adding an alkaline aqueous solution containing an alkali metal hydroxide and / or an alkaline earth metal hydroxide to the mixture of the activated silica and graphite. Process,
Is provided.

In the method for producing a silica / graphite unfired solidified body of the present invention, activated silica is obtained by forming an activated layer in which the surface of silica particles is mechanochemically activated by grinding silica in a dry process. (Activation step). This process causes the silica particles of the powder to undergo impact stress and shear stress due to grinding, resulting in changes in the chemical bond and electron density distribution, causing various chemical reactions due to charge transfer locally, and thermal processes. Unlike the excited state, the electron energy is excited to form a chemically activated activation layer. In addition, since this activation step is performed in a dry process, mechanochemical activation occurs only on the surface, and the interior remains in its original structure, so that the internal mechanical strength hardly decreases.
Further, as a mixing step, graphite is added to the powder composed of silica particles and mixed. Either the mixing step or the activation step may be performed first, or the mixing step and the activation step can be performed simultaneously (in this case, the silica and graphite are mixed and activated on the surface of the silica particles). A layer is formed). Graphite is a hexagonal system and has a layered structure, and the layers are bonded with a weak van der Waals force between the layers (between faces). For this reason, in this mixing process, it peels in layers as a very small flake.
In addition, an alkali aqueous solution containing an alkali metal hydroxide and / or an alkaline earth metal hydroxide was added to a mixture of silica powder and graphite on which an activated layer was formed, so that it was formed only on the surface of the particles. The activated layer is dissolved and reprecipitated to obtain a solidified body (solidification step). The solidified product thus obtained has a high mechanical strength due to the three-dimensional network structure formed by the activated layers bonded by dehydration condensation. In addition, the electrical conductivity is effectively increased by extremely small graphite flakes that are concentrated in the three-dimensional network structure.

  Examples of the alkali metal hydroxide contained in the aqueous alkali solution in the solidification step of the method for producing a silica / graphite non-fired solidified body of the present invention include potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. Examples of the alkaline earth metal hydroxide contained in the alkaline aqueous solution in the dissolving step include calcium hydroxide and barium hydroxide.

  The mixing process preferably includes a wet mixing process in which the mixing is performed in a wet process. This is because the graphite is mixed while being wetted with the solvent, so that it has an effect of preventing the aggregation of the graphite and enables more excellent dispersion.

  It is preferable to use a plurality of types of silica having different average particle diameters. If this is the case, the silica / graphite unfired solidified body with superior mechanical strength can be obtained by inserting the silica having a smaller average particle diameter into the gap formed when the activated silica having a larger average particle diameter come into contact with each other. It becomes. In addition, since silica having a large average particle diameter effectively plays a role as an abrasive for peeling between graphite layers in the mixing step, the grinding efficiency is improved. For this reason, many graphite particles are included and dispersed in the activated layer bonded by dehydration condensation, and as a result, a solidified body having high electric conductivity can be obtained.

  Moreover, if the average particle diameter of 1st silica particle is made into 10 times or more of the average particle diameter of 2nd silica particle among several types of silica particles, 2nd silica particle will be 1st silica particles. , The silica / graphite unfired solidified body is further excellent in mechanical strength.

  In the method for producing a silica / graphite non-fired solidified body of the present invention, the value of (volume of graphite as raw material) / (volume of silica as raw material + volume of graphite as raw material) is 0.1 or more and 0.00. It is preferable that it is 6 or less. If this value is less than 0.1, the mechanical strength and electrical conductivity may be insufficient. Moreover, when this value exceeds 0.6, there exists a possibility that mechanical strength and electrical conductivity may become inadequate.

It is process drawing which shows the manufacturing method of a silica / graphite non-baking solidified body. It is a schematic cross section of activated silica 1 having an activation layer 1a whose surface is mechanochemically activated. It is a schematic diagram which shows the state which the activated layer 1a of the surface of the activated silica 1 melt | dissolved and reprecipitated and solidified. It is an expansion schematic diagram of the precipitation layer 2a part shown in FIG. It is a schematic diagram which shows the solidified state at the time of using two types of activated silica from which an average particle diameter differs. FIG. 3 is a process diagram for producing the silica / graphite unfired solidified body of Example 1. It is an optical microscope photograph of the mixture after mixing process S22 in the manufacturing process of the silica / graphite unfired solidified body of Example 1. 4 is a graph showing the relationship between the volume percentage of graphite and the three-point bending strength in the silica / graphite unfired solidified body of Example 1. 2 is a graph showing the relationship between the volume percentage of graphite and the electrical conductivity in the silica / graphite unfired solidified body of Example 1. FIG. 2 is a scanning electron microscope (SEM) image of the silica / graphite non-fired solidified body of Example 1. FIG. It is the transmission electron microscope (TEM) image of the silica / graphite unfired solidified body of Example 1, and the EDS surface analysis image of the same location. 4 is a process diagram for producing a silica / graphite unfired solidified body of Example 2. FIG. 6 is a graph showing the relationship between the volume percentage of graphite and the three-point bending strength in the silica / graphite unfired solidified body of Example 2. 4 is a graph showing the relationship between the volume% of graphite and the electric conductivity in the silica / graphite unfired solidified body of Example 2. FIG. 4 is a process diagram for producing a silica / graphite unfired solidified body of Example 3. 6 is a graph showing the relationship between the volume percentage of graphite and the three-point bending strength in the silica / graphite unfired solidified body of Example 3. 4 is a graph showing the relationship between the volume percentage of graphite and the electrical conductivity in the silica / graphite unfired solidified body of Example 3. It is a photograph which shows the result of a water resistance test.

<Raw materials>
As raw materials for the silica / graphite unfired solidified body of the present invention, powder made of silica and graphite are used.
The type of silica is not particularly limited, and examples thereof include silica obtained by burning silicon, silica sand, dry silica (anhydrous silicic acid), wet silica (hydrous silica), and the like. From the viewpoint of strength, crystalline silica is preferred.
Moreover, there is no limitation in particular as a kind of graphite, For example, natural graphite and artificial graphite can be used.

-Manufacturing method of unfired solidified body of silica / graphite-
A process diagram of a method for producing a silica / graphite unfired solidified body is shown in FIG. Each step will be described in detail below.

<Activation step 11>
Prepare silica and grind it dry. As a result, as shown in FIG. 2, the activated silica particles 1 having the silica particles 1 b inside and the outer shells of which are mechanochemically activated activated layers 1 a are obtained. In the activated layer 1a, the network structure of silica is cut to form radicals or silanol groups are formed, 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. When pulverizing with a jet pulverizer, compressive force, shearing force, impact force and the like can be applied, whereby silica on the particle surface can be activated.

  In the activation step S11, it is preferable to grind until there is no change with time in the particle size distribution. Grinding until there is no change in the particle size distribution over time is considered to have reached the limit that the particles can be made fine by grinding, and the mechanochemical activation of the particle surface is the most advanced state. The activated silica 1 obtained by grinding to such a state is likely to proceed with dissolution with an alkaline aqueous solution, and the obtained silica / graphite unfired solidified product is dense and has high mechanical strength.

<Mixing step S12>
Next, graphite powder is added to the silica made of activated silica 1 obtained in the activation step 11 and mixed. By this step, the activated silica 1 acts as an abrasive, and the graphite powder is exfoliated in layers as extremely small flakes between layers bonded with a weak van der Waals force.
Unlike the process of FIG. 1, the mixing process is performed before the activation process, or the mixing process and the activation process are performed simultaneously (that is, silica is activated while mixing silica and graphite). ), The mixing step and the activation step may be repeated.
Moreover, when performing a mixing process in the wet, it is preferable that a solvent is a solvent which does not react with the activation layer 1a from a viewpoint that the activation layer 1a is not deactivated. Examples of such a solvent include ethanol, methanol, acetone, hexane, and toluene.

<Solidification step S13>
An alkaline aqueous solution containing an alkali metal hydroxide and / or an alkaline earth metal hydroxide is added to the mixed powder obtained in the above-described mixing step S11 for treatment. The apparatus for mixing and kneading the alkaline aqueous solution and the mixed powder 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. If it is like this, it can prevent that a bubble remains in a silica / graphite non-baking solidified body and mechanical strength falls.

  By this treatment, the activated layer 1a on the surface of the activated silica 1 in FIG. 2 is dissolved, and the adjacent layers are bonded by dehydration condensation to form a deposited layer 2a shown in FIG. At this time, the graphite particles 3 exfoliated very finely in the graphite added in the mixing step S11 are taken into the precipitation layer 2a (graphite 3 in FIG. 3) to form a composite (see FIG. 4). Thus, the precipitated layer 2a serves as an adhesive, and the silica / graphite non-fired solidified body 2 is obtained. In this solidifying step, the dissolution reaction of the activation layer 1a and the dehydration condensation reaction may be performed at room temperature, or may be accelerated by heating. The reaction temperature may be appropriately selected depending on the type of particles used as the raw material and the type and concentration of the aqueous alkali solution. In general, the reaction temperature is preferably from room temperature to 200 ° C, more preferably from room temperature to 60 ° C.

  In addition, it is also preferable to use a plurality of types of activated silica having different average particle diameters. If this is the case, as shown in FIG. 5, the silica 5 having a smaller average particle diameter enters the gap formed when the silicas 4 having a larger average particle diameter come into contact with each other. Silica / graphite unfired solidified product. In addition, silica having a large average particle size can effectively perform separation between the graphite layers in the mixing step, so that the grinding efficiency is improved and many graphites are added to the activated layer bonded by dehydration condensation. The particles are encapsulated and dispersed, and as a result, a solidified body having high electrical conductivity can be obtained.

  Furthermore, if the average particle diameter of the first activated silica among the plurality of types of activated silica is 10 times or more the average particle diameter of the second activated silica, the second activated silica is the first activated silica. Since it becomes easy to enter due to a gap formed by contact between the activated silicas, a silica / graphite non-fired solidified body having further excellent mechanical strength is obtained.

  The silica / graphite unfired solidified body obtained as described above is a silica / graphite unfired solidified body excellent in heat resistance and mechanical strength. In addition, since the conductive layer is dispersed in the precipitation layer 2a in which the activation layer 1a is dehydrated and condensed and bonded, it has excellent electrical conductivity.

Hereinafter, examples embodying the present invention will be described in detail.
Example 1
In Example 1, a silica / graphite unfired solidified body was produced by the process shown in FIG. Details will be described below.

<Activation step S21>
Silica fine powder 10 (average particle size 250nm, manufactured by Admatechs Co., Ltd., spherical silicon dioxide, trade name: Admafine) 30g was placed in a 250mL zirconia ball mill pot, and two zirconia balls (2 x 15mm in diameter and 5mm in diameter) 50 g), and dry pulverized at 200 rpm for 15 minutes to form a mechanochemically activated activation layer on the surface of the silica fine powder 10.

<Mixing step S22>
Volume of silica fine powder 10 having an activated layer mechanochemically activated on the surface by the activation step S21 and graphite 11 (average particle diameter 20 μm, manufactured by Ito Graphite Industries Co., Ltd., trade name: AGB-20) It put into the ball mill so that ratio might become a predetermined | prescribed ratio, and it mixed by the dry type. A 250 mL zirconia ball mill pot, two 15 mm zirconia balls and a diameter of 5 mm and 50 g were used for mixing. The rotation speed was 150 rpm. The ball mill time was 5 minutes, 15 minutes, 30 minutes, 60 minutes, 120 minutes, 300 minutes and 17 hours. An optical micrograph of the mixture thus obtained is shown in FIG. From this photograph, it can be seen that the silica particles are present in an aggregated state when the ball mill time is 5 minutes, 15 minutes and 30 minutes. In addition, as the time increased to 30 minutes and 60 minutes, the silica agglomerate size became smaller, and in 120 minutes and 300 minutes, silica agglomerated particles could not be observed and could be uniformly mixed with carbon. I understood that.

<Alkali addition step S23>
To the mixture obtained in the mixing step S22, a 3M potassium hydroxide aqueous solution was added to the whole, and wet mixing was performed until no aggregation occurred. The working time was 5 minutes.

<Defoaming step S24 and casting step S25>
Then, using a rotary defoamer, defoaming was performed at a rotation speed of 1000 rpm for 5 min and at atmospheric pressure. (Defoaming step S24). The obtained mixture was immediately cast into a fluororesin mold (casting step S25).

<Solidification step S26>
And in order to prevent drying, it used the air thermostat in the sealed state, and it heated at the temperature of 80 degreeC for 5 hours, and solidified the inside of a mold.

<Mold release step S27 and drying step S28>
The mold was removed (mold release step S27), and drying was performed at 80 ° C. for 2 hours in a heating furnace (drying step S28), whereby the silica / graphite unfired solidified body 12 of Example 1 was obtained.

(Evaluation)
The silica / graphite unfired solidified body 12 of Example 1 obtained as described above was subjected to three-point bending strength measurement, electrical conductivity measurement, and observation with an electron microscope. The results are detailed below.

・ Measurement of three-point bending strength Three-point bending strength was measured in accordance with JISR1601 “Testing method for room temperature bending strength of fine ceramics”. The sample used for the measurement has a mixing time of 300 minutes in the mixing step S22 (see FIG. 6) in which the activated silica fine powder 10 and the graphite 11 are mixed. As a result, as shown in FIG. 8, when the volume percentage of graphite in the sample is up to 20%, the three-point bending strength rapidly increases and reaches about 21 MPa, and when graphite is further added, it gradually decreases. I understood. On the other hand, when a measurement was also performed on a sample having a mixing time of 120 minutes or less in the mixing step S22 (see FIG. 6), the peak intensity was lower than 21 MPa. From this result, it was found that the mixing time in the mixing step S22 is preferably longer than 2 hours in order to increase the three-point bending strength.

-Measurement of electrical conductivity Electrical conductivity was measured by the Van der Pauw method, which is a kind of DC four-terminal method. The sample used for the measurement has a mixing time of 300 minutes in the mixing step S22 (see FIG. 6) in which the activated silica fine powder 10 and the graphite 11 are mixed. As a result, as shown in FIG. 9, the electric conductivity is as low as 1 × 10 ⁻² s / cm when the graphite volume percentage is up to 10 volume%, whereas it is 1 × 10 ⁴ s / cm above 20 volume%. It was found that the electric conductivity suddenly jumped up around 20% by volume when it was over cm.
On the other hand, when a measurement was also performed on a sample having a mixing time of 120 minutes in the mixing step S22 (see FIG. 6), the electric conductivity suddenly jumped up to about 30% by volume of graphite.

-Observation result by electron microscope The scanning electron microscope (SEM) image was image | photographed about the silica / graphite unbaking solidified body 12 of Example 1 obtained as mentioned above. As a result, as shown in FIG. 10, it was found that spherical particles were encapsulated in a film-like substance, and the film-like substance was bound like a string. Further, it was observed that fine particles were dispersed in the film-like substance.
Furthermore, when a transmission electron microscope (TEM) image and an EDS surface analysis image (carbon Kα ray, oxygen Kα ray, silicon Kα ray, and potassium Kα ray) at the same location were photographed, as shown in FIG. The spherical particles observed in the image were found to be SiO ₂ . It was also found that the film-like substance contained a lot of carbon.
From the above results, the silica / graphite unfired solidified body 12 of Example 1 includes spherical particles made of SiO ₂ encapsulated in a film-like substance, and the film-like substance is bound like a string. I understood that. Further, it was found that carbon fine particles due to graphite were dispersed in the film-like substance.
Note that a slight amount of potassium was derived from KOH added in the alkali addition step S23, and it was expected that potassium was combined with a dissolved substance of SiO ₂ .

(Example 2)
The process of Example 2 is shown in FIG. In Example 2, the mixing step S22 (see FIG. 6) of graphite and activated silica in Example 1 was dry mixing by a ball mill, but this was replaced by mixing by hand-grip work in a plastic bag. Performed (mixing step S32). About the other process, it carried out similarly to Example 1, and obtained the silica / graphite unbaking solidified body 12 of Example 2 (it attaches | subjects the same code | symbol about the same process and structure, and abbreviate | omits description).

(Evaluation)
The silica / graphite unfired solidified body 13 of Example 2 obtained as described above was measured for three-point bending strength and electrical conductivity. The measurement method is the same as in the case of Example 1 described above.

  As a result, as shown in FIG. 13, as shown in FIG. 13, the three-point bending strength rapidly increases as the amount of graphite increases up to 20% as the amount of graphite increases up to 20%, and more graphite is added. Then it was found that it gradually decreased. However, the peak intensity in Example 1 was about 21 MPa, whereas in Example 2, the result was as low as about 16 MPa. The difference in process between Example 1 and Example 2 is the mixing process of graphite and activated silica (in Example 1, it was dry mixing by a ball mill, whereas in Example 2, it was hand-gripped in a plastic bag. From this, it was found that sufficient mixing under the dry method is effective for the mixing step of graphite and activated silica.

  In addition, as shown in FIG. 14, in the measurement of electrical conductivity, it was found that the electrical conductivity jumped suddenly when the amount of graphite added exceeded a certain value, as in Example 1. However, the jumping point was 20% by volume in Example 1, but 30% by volume in Example 2.

(Example 3)
In Example 3, as shown in FIG. 15, apart from silica fine powder (average particle diameter 250 nm), silica coarse powder (particle diameter 20 to 300 μm) was also used, and after performing the activation step for each silica, These were mixed and used. Details will be described below.
<Activation step S211>
Silica fine powder 10 (average particle size 250nm, manufactured by Admatechs Co., Ltd., spherical silicon dioxide, trade name: Admafine) 30g was placed in a 250mL zirconia ball mill pot, and two zirconia balls (2 x 15mm in diameter and 5mm in diameter) 50 g), and dry pulverized at 200 rpm for 15 minutes to form a mechanochemically activated activation layer on the surface of the silica fine powder 10.
<Activation step S212>
Put 30g of silica coarse powder 13 (average particle size 20μm or more and less than 300μm) into a 250mL zirconia ball mill pot, and then add zirconia balls (two 15mm diameter and 50g diameter 5mm). By pulverizing for a minute, an activated layer activated mechanochemically was formed on the surface of the silica fine powder 10.

<Wet mixing step S213>
Silica having an activation layer mechanochemically activated on the surface in the activation step S212 and graphite (average particle diameter 20 μm, manufactured by Ito Graphite Industries Co., Ltd., trade name: AGB-20) are zirconia having a capacity of 250 mL. It was placed in a ball mill pot, and ethanol was added until fluidization was possible. Further, wet mixing was performed using zirconia balls (2 mm diameter, 5 mm diameter 50 g). The graphite particles were adjusted to 10, 20, 30, 40, 50, 60, 70, 80, and 90% by volume with respect to the total of fine silica powder and coarse powder. The mixing conditions were 24 h and 150 rpm.

<Drying step S214>
Ethanol in the dispersion mixture obtained in the wet mixing step S213 was removed by a rotary evaporator.

<Activation step S22>
The silica fine powder with the activated layer formed on the surface obtained in the activation step S211 and the silica coarse powder with the activated layer formed on the surface after the drying step S214 are put into a 250 mL zirconia ball mill pot and dried. Dispersion / mixing was performed. The ball mill conditions were set to 2 zirconia balls φ15 mm, φ5 mm 25 g, 2 h, 150 rpm for 30 g of powder. At this time, the mixing of the silica fine powder and the silica coarse powder was carried out at a volume ratio of 3: 7, 5: 5, and 7: 3.
Subsequent steps are the same as those in the first embodiment, and the same steps and configurations are denoted by the same reference numerals and description thereof is omitted.

(Evaluation)
The silica / graphite unfired solidified body 13 of Example 3 obtained as described above was measured for three-point bending strength and electrical conductivity. The measurement method is the same as in the case of Example 1 described above.

  As a result, as shown in FIG. 16, the three-point bending strength is 72 Mpa at 0% by volume of graphite, and gradually decreases as the volume% of graphite increases, but maintains 48 Mpa at 80% by volume. Thus, it was dramatically improved as compared with the case of Example 1 and Example 2. Unlike Example 1 and Example 2, Example 3 uses crystalline silica coarse powder, which is likely to cause surface activation due to a mechanochemical effect, which greatly increases the three-point bending strength. Probable cause.

  In addition, as shown in FIG. 17, in the measurement of electric conductivity, as in the case of Example 1, it was found that the electric conductivity jumped suddenly when the added amount of graphite exceeded a certain value. However, the jumping point was 20% by volume in Example 1, but 10% by volume in Example 2. From this, it was found that it is preferable to use crystalline coarse silica together with fine silica powder from the viewpoint of increasing electrical conductivity.

  In addition, the silica / graphite unfired solidified body of Example 3 (however, the volume ratio of silica fine powder 10 to silica coarse powder 13 is 30:70, the KOH concentration in the alkali addition step S23 is 2M, and the heating temperature in the solidification step S26 is The thermal conductivity was measured for 80 ° C. and the heating time was 4 hours. For comparison, the silica / graphite non-fired solidified body of Example 1 (however, the KOH concentration in the alkali addition step S23 is 2M, the heating temperature in the solidification step S26 is 80 ° C., and the heating time is 4 hours). Thermal conductivity was also measured. As a result, as shown in Table 1, although both samples improved in thermal conductivity with an increase in the graphite content, Example 3 in which the silica fine powder 10 and the silica coarse powder 13 were used in combination had the silica fine powder 10 It was found that the thermal conductivity was superior to that of Example 1 in which only silica was used as the silica source. This is presumed to be due to the increase in the amount of material contained in the film-like substance and the stringing structure shown in FIG. The

  In addition, the silica / graphite unfired solidified body of Example 3 (however, the volume ratio of silica fine powder 10 to silica coarse powder 13 is 30:70, the KOH concentration in the alkali addition step S23 is 1M, and the graphite volume percentage is 20%. , 50% and 80%) were subjected to a water resistance test (immersion in water for a long time). For comparison, solidified bodies were also prepared for those added with water instead of KOH in the alkali addition step S23, and the same water resistance test was performed. As a result, as shown in FIG. 18, in the silica / graphite non-fired solidified body of Example 3, no change was observed even after immersion in water for 1 week. On the other hand, what solidified with water instead of KOH had disintegrated after only 3 minutes.

  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.

  The silica / graphite non-fired solidified body of the present invention is excellent in mechanical strength, heat resistance and thermal conductivity, and can be used for materials such as heat sinks and brake pads.

10, 13 ... silica (10 ... fine silica powder, 13 ... coarse silica powder)
3, 11 ... Graphite 1 ... Activated silica (1b ... Inner core particle, 1a ... Activated layer)
2,12,13,14 ... Silica / graphite unfired solidified body S11, S21, S211, S212, S22 ... Activation step S12, S213, ... Mixing step (S11 ... Mixing step, S213 ... Wet mixing step)
S13, S26 ... Solidification process

Claims (8)

An activated silica having inner core particles made of silica and an activated layer mechanochemically activated that forms an outer shell of the inner core particles is bonded to each other by dehydration condensation to form a solidified body. ,
Silica / graphite unfired solidified body in which graphite particles are encapsulated and dispersed in the activated layer bonded by dehydration condensation.   The silica / graphite non-fired solidified body according to claim 1, wherein an average particle diameter of the graphite particles is 50 nm or less.   3. The silica / graphite unfired solid body according to claim 1, wherein the solidified body includes graphite particles that are not dispersed in the activated layer bonded by the dehydration condensation. 4. An activation step in which silica is ground in a dry process to form activated silica in which an activated layer in which the surface of the silica particles is mechanochemically activated is formed;
A mixing step of adding graphite to the activated silica and mixing;
Solidification to obtain a solidified body by dissolving and reprecipitating the activated layer by adding an alkaline aqueous solution containing an alkali metal hydroxide and / or an alkaline earth metal hydroxide to the mixture of the activated silica and graphite. Process,
A method for producing a silica / graphite non-fired solidified body comprising:   The method for producing an unfired solidified body of silica / graphite according to claim 4, wherein the mixing step includes a wet mixing step of mixing in a wet manner.   The method for producing a silica / graphite unfired solidified body according to claim 4 or 5, wherein a plurality of types of silica having different average particle diameters are used.   The silica / graphite non-fired solidification according to claim 6, wherein the average particle diameter of the first activated particles among the plurality of types of activated particles is 10 times or more the average particle diameter of the second activated particles. Body manufacturing method.   The value of (volume of graphite as a raw material) / (volume of silica as a raw material + volume of graphite as a raw material) is 0.1 or more and 0.6 or less. A method for producing an unfired solidified product of silica / graphite.