KR20210059932A - Moisture adsorption filter for gas sensor based on anodic aluminum oxide substrate using ultrasonic spray method and method of manufacturing the same - Google Patents

Abstract

Disclosed are a moisture adsorption filter for a gas sensor based on an anodic aluminum oxide (AAO) substrate using an ultrasonic spray method and a method of manufacturing the same that can exhibit excellent adsorption performance by coating a silica gel precursor solution using particulate silica gel powder as a raw material on the surface of an AAO substrate using an ultrasonic spray method to form a moisture adsorption layer. A method of manufacturing a moisture adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to the present invention includes the steps of: preparing silica gel powder; mixing the silica gel powder with a solvent and stirring to form a silica gel precursor solution; and forming a moisture adsorption layer by filling the silica gel precursor solution into a syringe of an ultrasonic coating machine, and then coating it on the AOA substrate by ultrasonic spraying.

Description

Water adsorption filter for gas sensor based on AAO substrate using ultrasonic spray method and its manufacturing method {MOISTURE ADSORPTION FILTER FOR GAS SENSOR BASED ON ANODIC ALUMINUM OXIDE SUBSTRATE USING ULTRASONIC SPRAY METHOD AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method, and a method of manufacturing the same, and more particularly, a silica gel precursor solution made of silica gel powder in the form of fine particles as a raw material is applied to an ultrasonic spray method. The present invention relates to a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method capable of exerting excellent adsorption performance by forming a moisture adsorption layer by coating on the surface of an AAO substrate by using, and a method of manufacturing the same.

When most electronic devices come into contact with moisture, corrosion and durability problems occur. Therefore, research on a moisture filter for blocking such moisture is actively in progress.

For example, in a gas sensor for sensing gas in the atmosphere, moisture in the air penetrates into the inside of an electronic device, causing not only failure of the gas sensor electronic devices, but also has a great influence on sensing sensitivity.

Fiber filters are mainly used as conventional moisture adsorption filters. However, in the case of such a fiber filter, there is a limitation in the adsorption performance and there is difficulty in manufacturing.

As a related prior document, there is Korean Patent Laid-Open Publication No. 10-2008-0045626 (published on May 23, 2008), which discloses an ion exchange type lithium adsorbent using a ceramic filter and a method of manufacturing the same.

It is an object of the present invention to form a moisture adsorption layer by coating a silica gel precursor solution made of fine particles of silica gel powder as a raw material on the surface of an AAO substrate using an ultrasonic spray method, thereby exhibiting excellent adsorption performance. It is to provide a water adsorption filter for a gas sensor based on an AAO substrate using a spray method and a method of manufacturing the same.

A method of manufacturing a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to an embodiment of the present invention for achieving the above object comprises: preparing a silica gel powder; Mixing and stirring the silica gel powder in a solvent to form a silica gel precursor solution; And forming a moisture adsorption layer by filling the silica gel precursor solution into a syringe of an ultrasonic coating machine and then coating it on the AOA substrate using an ultrasonic spray method.

The silica gel precursor solution includes 5 to 20% by weight of silica gel powder and 80 to 95% by weight of a solvent.

It is preferable to use at least two or more of the silica gel powder having different average diameters.

The silica gel powder is more preferably a mixture of a first silica gel powder having an average diameter of 30 µm or less and a second silica gel powder having an average diameter of 50 µm or more.

The first silica gel powder and the second silica gel powder are added in a weight ratio of 2:8 to 8:2.

The solvent is ethanol, acetone, dimethylformamide (DMF), octanol, tetradecane, pentanol, dipropylene glycol monomethyl ether, and ethylene. It may contain at least one selected from among glycols (ethylene glycol).

The ultrasonic spray coating is performed in a frequency range of 70 to 90 Hz.

The silica gel precursor solution is preferably sprayed at a rate of 0.5 to 2.0 mL/h.

In addition, the ultrasonic spray coating is performed at 70 to 90°C for 10 to 240 sec.

The ultrasonic spray coating is performed in a state in which the spray nozzle of the ultrasonic coating machine and the AAO substrate are kept at a separation distance of 5 to 10 cm.

A water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to an embodiment of the present invention for achieving the above object comprises: an AAO substrate; And a moisture adsorption layer formed by coating on the AAO substrate by an ultrasonic spray method, wherein the moisture adsorption layer ultrasonically sprays a filter precursor solution containing 5 to 20% by weight of silica gel powder and 80 to 95% by weight of a solvent. It is characterized in that it is formed by coating and curing in a manner.

Here, the moisture adsorption layer has a thickness of 50 μm or less.

In addition, the moisture adsorption filter has a specific surface area of 680 to 730 m 2 /g.

A water adsorption filter for a gas sensor based on an AAO substrate using the ultrasonic spray method according to the present invention and a method of manufacturing the same are prepared by coating a silica gel precursor solution mixed with a silica gel powder in a solvent on an AAO substrate by an ultrasonic spray coating method. As a result, excellent moisture adsorption ability can be exhibited, and since the moisture adsorbed at about 80° C. is desorbed again due to the nature of the silica gel powder, reuse may be possible.

In addition, the water adsorption filter for a gas sensor based on an AAO substrate using the ultrasonic spray method according to the present invention and a method of manufacturing the same are not a fiber filter method, but a silica gel precursor solution obtained by mixing silica gel particles in a solvent using an ultrasonic spray method. Since a moisture adsorption layer is formed by coating, a moisture adsorption filter can be manufactured with a thinner thickness.

In addition, the water absorption filter for gas sensors based on the AAO substrate using the ultrasonic spray method according to the present invention and the method of manufacturing the same are directly coated on the AAO substrate by the ultrasonic spray method, so that not only the production of the water absorption layer is easy, but also large area Because it is easy, it may become possible to apply it to a variety of electronic devices.

1 is a process flow chart showing a method of manufacturing a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to an embodiment of the present invention.
2 is a cross-sectional view illustrating an ultrasonic spray coating process of FIG. 1.
3 is a schematic diagram of a process for explaining the ultrasonic spray coating process of FIG. 1.
4 is a view for explaining the ultrasonic spray coating process conditions of FIG.
5 is a graph showing the weight measurement results for each coating time of a moisture adsorption filter manufactured using 20 μm silica gel particles.
6 is a graph showing the measurement of moisture adsorption rate and moisture desorption rate by coating time of a moisture adsorption filter manufactured using 20 μm silica gel particles.
7 is a graph showing the measurement of the moisture adsorption rate and the moisture desorption rate according to the silica gel particle ratio.
8 is a graph showing the moisture adsorption rate and moisture desorption rate by coating time at the optimum mixing ratio of silica gel particles.
9 is a graph showing the air permeability measurement result according to the silica gel particle ratio.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described later in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, only this embodiment is intended to complete the disclosure of the present invention, and the general knowledge in the technical field to which the present invention pertains. It is provided to completely inform the scope of the invention to the possessor, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

Hereinafter, a moisture adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to a preferred embodiment of the present invention and a method of manufacturing the same will be described in detail with reference to the accompanying drawings.

1 is a process flow chart showing a method of manufacturing a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to an embodiment of the present invention, and FIG. 2 is a process cross-sectional view for explaining the ultrasonic spray coating process of FIG. . In addition, FIG. 3 is a schematic diagram illustrating the ultrasonic spray coating process of FIG. 1, and FIG. 4 is a diagram illustrating the ultrasonic spray coating process conditions of FIG. 1.

As shown in FIG. 1, a method of manufacturing a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to an embodiment of the present invention includes a silica gel powder preparation step (S110), a silica gel precursor solution formation step (S120). ) And an ultrasonic spray coating step (S130).

Preparation of silica gel powder

In the silica gel powder preparation step (S110), silica gel powder is prepared.

At this time, the silica gel powder is silicon dioxide having extremely high porosity. At this time, since the silica gel powder is porous, it is easy to adsorb moisture. Accordingly, the silica gel powder may have a plurality of pores therein.

For this reason, silica gel powder has a better moisture adsorption ability than that of zeolite and activated carbon. Therefore, when silica gel powder is used as an adsorbent, the adsorption performance can be further improved.

However, if silica gel powder is used directly as a moisture adsorption filter, its moisture adsorption ability is excellent, but its use is limited due to its excessive thickness. To solve this problem, in the present invention, a silica gel precursor solution was formed by adding silica gel powder in the form of fine particles to a solvent, and then the silica gel precursor solution was coated on the AAO substrate by ultrasonic spray coating to prepare a moisture adsorption filter.

At this time, it is preferable to use at least two or more silica gel powders having different average diameters. As for the silica gel powder, it is more preferable to use a mixture of a first silica gel powder having an average diameter of 30 µm or less and a second silica gel powder having an average diameter of 50 µm or more.

As described above, when the first silica gel powder of a small size and the second silica gel powder of a large size are mixed and used, the moisture adsorption ability is better than when a single size silica gel powder is used. This is because the specific surface area is more increased when the first and second silica gel powders are mixed.

Here, the first silica gel powder and the second silica gel powder are preferably added in a weight ratio of 2:8 to 8:2. At this time, it was confirmed through an experiment that the optimum weight ratio of the first and second silica gel powder was 7.5:2.5. When the mixing ratio of the first and second silica gel powder is less than 2:8 or exceeds 8:2, adsorption performance may be deteriorated due to a decrease in specific surface area.

Silica gel precursor solution formation

In the silica gel precursor solution forming step (S120), silica gel powder is mixed with a solvent and stirred to form a silica gel precursor solution.

At this time, the solvent is ethanol, acetone, DMF (dimethylformamide), octanol, tetradecane, pentanol, dipropylene glycol monomethyl ether, and It may contain at least one selected from ethylene glycol.

In this case, the silica gel precursor solution preferably contains 5 to 20% by weight of the silica gel powder and 80 to 95% by weight of the solvent.

Ultrasonic spray coating

1 to 4, in the ultrasonic spray coating step (S130), a silica gel precursor solution is filled into the spray nozzle 240 of the ultrasonic coater 200, and then the AOA substrate 110 is applied by an ultrasonic spray method. The moisture adsorption layer 120 is formed by coating on.

Here, the AAO substrate (anodic aluminum oxide substrate) 110 refers to an aluminum substrate in which holes having a size of approximately 10 to 100 nm are regularly arranged on the surface by anodizing of aluminum. Accordingly, when the moisture adsorption layer 120 is directly formed on the AAO substrate 110 having nano-sized pores by the ultrasonic spray coating method, it has a structural advantage of maximizing adsorption efficiency.

The ultrasonic coating machine 200 includes a hot plate support plate 210 supporting a hot plate 220 for heating the AAO substrate 110, an ultrasonic coating machine body 230 for generating ultrasonic waves, and a silica gel precursor using an ultrasonic spray method. A spray nozzle 240 for spraying the solution onto the AAO substrate 110 and a syringe pump 250 for controlling a supply amount of the silica gel precursor solution supplied to the spray nozzle 240 may be included.

In addition, the ultrasonic coating machine 200 may further include a power supply wiring 260 having one end electrically connected to the ultrasonic coating machine body 230 and the other end electrically connected to the spray nozzle 240.

In this step, the ultrasonic spray coating is preferably carried out in the frequency range of 70 ~ 90Hz.

At this time, the silica gel precursor solution is preferably sprayed at a rate of 0.5 to 2.0 mL/h. If the spraying speed is less than 0.5 mL/h, the spray nozzle 240 may be clogged. Conversely, when the spraying rate exceeds 2.0 mL/h, there is a concern that the silica gel precursor solution may not be uniformly coated over the entire area.

In this step, the ultrasonic spray coating is preferably carried out at 70 ~ 90 ℃ for 10 ~ 240sec.

If the ultrasonic spray coating time is less than 10 sec, it may be difficult to properly exhibit the moisture adsorption ability. Conversely, when the ultrasonic spray coating time exceeds 240 sec, the specific surface area increases, but the air permeability decreases, making it difficult to use as a filter.

In addition, the ultrasonic spray coating is preferably performed in a state in which the spray nozzle 240 of the ultrasonic coating machine 200 and the AAO substrate 110 are kept at a separation distance of 5 to 10 cm. If the separation distance is less than 5 cm, there is a concern that the film quality characteristics are deteriorated due to interference by the spray nozzle 240. Conversely, when the separation distance exceeds 10 cm, it may be difficult to secure a uniform film.

By the above processes (S110 to S130), a moisture adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to an embodiment of the present invention may be manufactured.

As described so far, the water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to an embodiment of the present invention and a method of manufacturing the same include an ultrasonic spray coating method using a silica gel precursor solution obtained by mixing silica gel powder in a solvent. It can exhibit excellent moisture adsorption ability by coating it on the AAO substrate and making it possible to reuse it because the moisture adsorbed at about 80°C is desorbed again due to the characteristics of the silica gel powder.

In addition, the water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method according to an embodiment of the present invention and a method of manufacturing the same are not a fiber filter method, but a silica gel precursor solution obtained by mixing silica gel particles in a solvent by ultrasonication. Since the moisture adsorption layer is formed by coating in a spray method, a moisture adsorption filter can be manufactured with a thinner thickness.

In addition, the water absorption filter for gas sensors based on the AAO substrate using the ultrasonic spray method according to the embodiment of the present invention and the manufacturing method thereof are directly coated on the AAO substrate by the ultrasonic spray method, so it is not only easy to manufacture the water absorption layer, Since it is easy to increase the area to a large area, it may become possible to apply it to various electronic devices.

As a result, the moisture adsorption layer according to the embodiment of the present invention may have a very thin thickness of 50 μm or less.

In addition, the water adsorption filter for a gas sensor based on an AAO substrate using the ultrasonic spray method according to an embodiment of the present invention has a specific surface area of 680 to 730 m 2 /g.

In addition, the moisture adsorption filter for a gas sensor based on an AAO substrate using the ultrasonic spray method according to an embodiment of the present invention exhibits a moisture desorption rate of about 97% or more when desorption at 80°C for 1 hour, and moisture when maintained for 3 hours or more. Desorption rate may represent about 99% or more.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this has been presented as a preferred example of the present invention and cannot be construed as limiting the present invention in any sense.

Contents not described herein can be sufficiently technically inferred by those skilled in this technical field, and thus description thereof will be omitted.

1. Sample preparation

Silica gel particles each having an average diameter of 100 μm and an average diameter of 20 μm were prepared.

Next, 10 g of silica gel particles were added to 90 g of ethanol, followed by stirring for 24 hours.

Next, silica gel particles and ethanol were mixed with the stirred result in the composition ratio of Table 1, and then stirred for 24 hours to prepare a silica gel precursor solution, respectively.

Next, 12 ml of each silica gel precursor solution was put into a syringe, and then ultrasonic spray-coated and cured on the surface of the AAO substrate at a coating temperature of 80° C. using an ultrasonic coating machine to prepare a moisture adsorption filter.

Here, the ultrasonic spray coating was performed at a frequency of 80 Hz, a separation distance of 8 cm between the spray nozzle and the AAO substrate, and a feed rate of 1 mL/h.

[Table 1]

2. Property evaluation

Table 2 shows the weight measurement result of the moisture adsorption filter manufactured using 20 μm silica gel particles by coating time, and FIG. 5 is the weight measurement result of the moisture adsorption filter manufactured using 20 μm silica gel particles by coating time It is a graph showing.

[Table 2]

As shown in Table 2 and FIG. 5, the result of measuring the weight change of the moisture adsorption filter manufactured using 20 μm silica gel particles is shown.

At this time, it can be seen that the weight increases gradually as the coating time increases. It is believed that this is because as the coating time increases, the number of silica gel particles coated on the AAO substrate increases.

Table 3 shows the moisture adsorption rate and moisture desorption rate by coating time of the moisture adsorption filter manufactured using 20 μm silica gel particles, and FIG. 6 is a moisture adsorption filter manufactured using 20 μm silica gel particles. It is a graph showing the moisture adsorption rate and moisture desorption rate measured by coating time of.

[Table 3]

As shown in Table 3 and FIG. 6, measurement results of the moisture adsorption rate and moisture desorption rate by coating time of the moisture adsorption filter manufactured using 20 μm silica gel particles are shown.

At this time, it can be seen that the moisture adsorption rate increases as the coating time increases. It is judged that the moisture adsorption rate increases because the number of coated silica gel particles increases as the coating time increases.

In addition, the moisture desorption rate exhibited a moisture desorption rate of about 97% or more when desorption at 80° C. for 1 hour, and when maintained for 3 hours or more, the moisture desorption rate was 99% or more. Therefore, it was confirmed that reuse is possible when exposed to 80° C. for about 3 hours or more.

7 is a graph showing the measurement of the moisture adsorption rate and the moisture desorption rate according to the silica gel particle ratio.

As shown in Table 1 and FIG. 7, as a result of measuring the moisture adsorption rate and moisture desorption rate according to the silica gel particle ratio, the moisture adsorption ability is excellent as the coating time increases in all samples. It was confirmed that 100% desorption was performed at 80°C.

In particular, the moisture adsorption rate was the best at the composition ratio of silica gel 20 µm + 100 µm = 7.5: 2.5.

In addition, it was confirmed that the moisture adsorption ability was better when silica gel particles of different sizes were mixed than when the silica gel particles were coated with a single size.

In addition, as a result of measuring the specific surface area, it was confirmed that the moisture adsorption ratio is proportional to the specific surface area of the filter. At this time, it was found that the optimum range was when the mixing ratio of the silica gel particles was designed to be 7.5:2.5.

Table 4 shows the moisture adsorption rate and moisture desorption rate by coating time at the optimum mixing ratio of silica gel particles, and Table 5 shows the results of measuring the specific surface area by coating time at the optimum mixing ratio of silica gel particles. In addition, FIG. 8 is a graph showing a moisture adsorption rate and a moisture desorption rate by coating time at an optimum mixing ratio of silica gel particles, and FIG. 9 is a graph showing air permeability measurement results according to the silica gel particle ratio.

[Table 4]

[Table 5]

As shown in Table 4 and FIG. 8, the moisture adsorption rate and moisture desorption rate for each coating time when the silica gel particles are designed in an optimal mixing ratio of 7.5:2.5 are shown.

At this time, it can be seen that the moisture adsorption rate increases as the coating time increases. It is judged that the moisture adsorption rate increases because the number of coated silica gel particles increases as the coating time increases.

In addition, the moisture desorption rate exhibited a moisture desorption rate of about 99% or more when desorption at 80°C for 1 hour, and when maintained for 3 hours or more, the moisture desorption rate was 100%.

As shown in Table 5 and FIG. 9, as a result of measuring the specific surface area according to the coating time, as the nose time increased, the specific surface area increased and the moisture adsorption ability increased.

On the other hand, as a result of measuring the air permeability, it was concluded that coating with 150 sec was most appropriate because the air permeability was low and it was difficult to use it as a moisture adsorption filter when coating for more than 240 sec. At this time, when the air permeability exceeds 585 mm/sec (300 CFM), the filter effect is low, and when the air permeability is less than 80 mm/sec (15.00 CFM), the sensitivity is poor.

Although the above has been described with reference to the embodiments of the present invention, various changes or modifications can be made at the level of those of ordinary skill in the art to which the present invention pertains. Such changes and modifications may be said to belong to the present invention as long as they do not depart from the scope of the technical idea provided by the present invention. Therefore, the scope of the present invention should be determined by the claims set forth below.

110: AAO substrate 120: moisture absorption layer
210: hot plate support plate 220: hot plate
230: ultrasonic coating machine body 240: spray nozzle
250: syringe pump 260: power supply wiring
S110: silica gel powder preparation step
S120: silica gel precursor solution formation step
S130: ultrasonic spray coating step

Claims (15)

Preparing a silica gel powder;
Mixing and stirring the silica gel powder in a solvent to form a silica gel precursor solution; And
Filling the silica gel precursor solution into a syringe of an ultrasonic coating machine and then coating it on the AOA substrate using an ultrasonic spray method to form a moisture adsorption layer;
A method of manufacturing a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method comprising a.
The method of claim 1,
The silica gel precursor solution is
A method of manufacturing a moisture filter for a gas sensor based on an AAO substrate, characterized in that it comprises 5 to 20% by weight of silica gel powder and 80 to 95% by weight of a solvent.
The method of claim 2,
The silica gel powder is
A method of manufacturing a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method, characterized in that at least two or more having different average diameters are used.
The method of claim 2,
The silica gel powder is
Moisture adsorption for gas sensors based on AAO substrates using an ultrasonic spray method characterized by using a mixture of a first silica gel powder having an average diameter of 30 μm or less and a second silica gel powder having an average diameter of 50 μm or more Filter manufacturing method.
The method of claim 4,
The first silica gel powder and the second silica gel powder
A method of manufacturing a water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method, characterized in that it is added in a weight ratio of 2:8 to 8:2.
The method of claim 1,
The solvent is
Ethanol, acetone, DMF (dimethylformamide), octanol, tetradecane, pentanol, dipropylene glycol monomethyl ether, and ethylene glycol glycol), characterized in that it comprises at least one selected from the AAO substrate-based water adsorption filter for a gas sensor using an ultrasonic spray method.
The method of claim 1,
The ultrasonic spray coating is
A method of manufacturing a water adsorption filter for gas sensors based on an AAO substrate using an ultrasonic spray method, characterized in that carried out in a frequency range of 70 to 90 Hz.
The method of claim 1,
The silica gel precursor solution is
A method of manufacturing a water adsorption filter for gas sensors based on an AAO substrate using an ultrasonic spray method, characterized in that spraying at a rate of 0.5 to 2.0 mL/h.
The method of claim 1,
The ultrasonic spray coating is
A method of manufacturing a water adsorption filter for gas sensors based on AAO substrates using an ultrasonic spray method, characterized in that carried out at 70 to 90°C for 10 to 240 sec.
The method of claim 1,
The ultrasonic spray coating is
A method of manufacturing a moisture adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method, characterized in that it is carried out in a state in which the spray nozzle of the ultrasonic coating machine and the AAO substrate are maintained at a distance of 5 to 10 cm.
A water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method manufactured by the method according to claim 1,
AAO substrate; And
Includes; a moisture adsorption layer formed by coating on the AAO substrate by an ultrasonic spray method,
The moisture adsorption layer is formed by coating a filter precursor solution containing 5 to 20% by weight of silica gel powder and 80 to 95% by weight of a solvent by an ultrasonic spray method, and curing it. Moisture adsorption filter for gas sensors.
The method of claim 11,
The silica gel powder is
Moisture adsorption for gas sensors based on AAO substrates using an ultrasonic spray method characterized by using a mixture of a first silica gel powder having an average diameter of 30 μm or less and a second silica gel powder having an average diameter of 50 μm or more filter.
The method of claim 12,
The first silica gel powder and the second silica gel powder
A water adsorption filter for a gas sensor based on an AAO substrate using an ultrasonic spray method, characterized in that it is added in a weight ratio of 2:8 to 8:2.
The method of claim 11,
The moisture adsorption layer
A water adsorption filter for gas sensors based on an AAO substrate using an ultrasonic spray method, characterized in that it has a thickness of 50 μm or less.
The method of claim 11,
The moisture adsorption filter
Water adsorption filter for gas sensor based on AAO substrate using ultrasonic spray method, characterized in that it has a specific surface area of 680 ~ 730㎡/g.

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