JPH01257120A - Production of porous drying gel - Google Patents

Abstract

PURPOSE:To eliminate the occurrence of volume shrinkage and crack by washing wet gel obtd. from a hydrolyzate of silicon alkoxide by a specified method, with liq. CO2 and by removing the liq. CO2 through the supercritical state. CONSTITUTION:The hydrolyzate (sol) of silicon alkoxide such as Si(OC2H5)4, Si(OCH3)4, preferably hydrolyzate of Si(OC2H5)4, to which is added silica fine particles (50mum particle size), is subjected to ultrasonic wave to disperse the silica fine particles and centrifuged to remove huge particles. The wet gel is obtd. by controlling the obtd. sol in <=4pH value, preferably in 2.0-3.0, and at 5-10 deg.C. The wet gel is washed with liq. CO2 to substitute the volatile component in the gel body with liq. CO2. Thereafter, the porous drying gel is obtd. by bringing the gel body in the supercritical condition to remove the liq. CO2 in the gel body.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a porous dry gel produced using a metal alkoxide, particularly a silicon alkoxide, as a starting material.

[Conventional technology]

Conventional gel bodies made from silicon alkoxide have been manufactured for the purpose of vitrification after drying and heat treatment.

[Problem to be solved by the invention]

In the conventional technology, the purpose is to finally make the gel body non-porous after heat treatment, and the porous gel body during the manufacturing process is not utilized.

Therefore, when attempting to directly utilize the porous gel body obtained in the process according to the prior art, the following problems arise.

Porous gel bodies obtained by the sol-gel method generally have low strength, so if they are used directly, they must be reinforced with some kind of rigid body.

However, when a wet gel is used, there is a problem that the gel body shrinks in volume over time, resulting in separation from the rigid body or cracks in the gel body.

In addition, when trying to use a wet gel formed in or on a rigid body as a dry gel, volume shrinkage is large in the process from wet gel to dry gel, and in this case as well, separation from the rigid body and gel body There are problems such as crack formation.

For these reasons, it has not been possible to directly utilize porous gel bodies obtained by the sol-gel method.

The present invention has been made in view of the above, and an object of the present invention is to provide a method for producing a porous dry gel that can obtain a dry gel that does not undergo volume shrinkage or cracks compared to a wet gel. It is something to do.

[Means and effects for solving the problem] As a result of experiments to achieve the above object, the present inventors added silica fine particles to a hydrolysis product (sol) of tetraethoxysilane, which is a type of silicon alkoxide, as a wet gel. (particle size: 50 nm), the pH of the liquid is controlled to 4.0 or less, preferably 2.0 to 3.0, and the temperature is 5 to 10°C. This is then washed with liquid CO2. After replacing the volatile components in the gel body with liquid CO2, the liquid CO2 is removed through the supercritical state of CO□, thereby creating a dry gel that does not shrink in volume or generate cracks compared to wet gels. I discovered that you can get

Although tetramethoxysilane may be used instead of the above-mentioned tetraethoxysilane, it is preferable to use tetraethoxysilane from the viewpoint of speed of hydrolysis and condensation reactions. An aqueous HCI solution is added to the tetraethoxysilane (silicon alkoxide) while stirring vigorously. After stirring and reacting for 30 minutes, silica particles are added. The amount of silica fine particles added is one of the factors that determines the pore size of the gel body. Ultrasonic waves of 20 KHz are applied to the obtained silica fine particle-containing sol for 30 minutes or more to disperse the silica fine particles. This sol solution is centrifuged to remove large particles. The pH of the obtained sol solution is adjusted to 4.0 or less and gelatinized. At this time, when the pH is greater than 4.0, silica particles are dispersed in the gel body, whereas under the conditions of the present invention, the added silica fine particles undergo grain growth due to the alkoxide reactant, and At the same time, a skeleton structure of silica particles is formed. The formation of this configuration makes it possible to convert a wet gel into a dry gel without changing its porous structure by the method described below.

That is, the obtained wet gel is sufficiently washed with liquid CO□ to replace volatile components in the gel body with liquid CO2. Thereafter, the gel body is placed under CO2 supercritical conditions, and liquid CO2 in the gel body is quickly removed.

By the above operations, it is possible to obtain a dry gel having the same volume as the wet gel and without cracks.

〔Example〕

Examples of the present invention are shown below.

Example 1 Into 20 g of vigorously stirred tetraethoxysilane, 0.
05NH (14.1 ml aqueous solution) was added. After stirring for 30 minutes, silica fine particles 0X-
7.0g of 50 was added.

While maintaining this sol solution at 5° C., 20 KHz ultrasonic waves were applied for 30 minutes, and giant particles were removed using a 100OG centrifuge. Next, the pH was adjusted to 2.5 with a 0.5NH3 aqueous solution, and then maintained at 5° C. for 50 hours to form a gel. The obtained gel was heated at 5°C in a 5CE-500 supercritical extraction device manufactured by Sumitomo Heavy Industries.
, 150 kg/cj, liquid CO2, flow ffi 5 , 0
kg/hr.

After washing for 10 hours, the temperature was raised to 40°C in the same equipment.
Thereafter, the pressure was reduced to atmospheric pressure to remove liquid cO2. The obtained dry gel body has a pore size of approximately 1000 to 700 t.
It was a porous body of v. A SEM photograph of the particle structure of the fractured surface of the obtained gel body is shown in FIG.

Example 2 Into 20 g of vigorously stirred tetraethoxysilane, 0.
14.1 ml of 0.05N HCfI aqueous solution was added. After stirring for 30 minutes, silica particles 0X-
50 was added at 7.0 gfA. While maintaining this sol solution at 5°C, 20KHz ultrasonic waves were applied for 30 minutes, and 100O
Giant particles were removed using a G centrifuge. After adjusting the pH to 4.6 with a 0.5N NH3 aqueous solution, the mixture was maintained at 5°C for 10 hours to form a gel. The obtained gel was transferred to 5CE-5 manufactured by Sumitomo Heavy Industries.
After washing for 10 hours at 5° C., 150 kg/c♂, liquid CO2, flow m 5 , O kg/hr in a 00 supercritical extraction device, the temperature was raised to 40° C. in the same device, and the pressure was reduced to atmospheric pressure. Liquid CO2 was removed. The obtained dry gel body was a porous body with a pore diameter of approximately 600 nm or less. Further, the gel body at this time suffered volumetric shrinkage during the drying process.

A SEM photograph of the particle structure of the fractured surface of the gel body Q obtained is shown in FIG.

Example 3 Under the conditions of Example 1, 14 g of silica fine particles 0X-50 were added. The resulting dry gel body had a pore size of 800-400 ni.

〔Effect of the invention〕

According to the present invention, the porous dry gel can be prepared at a temperature of up to 40° C. during its treatment process, and at a temperature of up to 40° C., a strong acid, a strong base or
Do not use toxic chemicals.

Therefore, after adding various organic functional molecules, bacteria, etc. to the raw sol solution, it is possible to support the functional substances in a dry gel body by the method of the present invention without impairing their activity.

Therefore, it is possible to obtain highly functional gel materials that have extremely high utility value, such as ion sensors using ion-sensitive organic substances, carriers for bacteria in bioreactors, and the like.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are photographs showing the particle structures of fractured surfaces of gel bodies obtained in different examples. Applicant Komatsu Manufacturing Co., Ltd. Representative Patent Attorney Masaaki Yonehara

Claims (1)

[Claims] Fine silica particles are added to a hydrolysis product (sol) of silicon alkoxide such as tetraethoxysilane or tetramethoxysilane, and the pH of the liquid is set to 4.0 or less to produce a wet gel. A method for producing a porous dry gel, which comprises washing with CO_2 to replace volatile components in the gel body with liquid CO_2, and then removing liquid CO_2 from the gel body through the supercritical state of CO_2.