JPH06510268A - Silica airgel-like material manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Production of silica airgel-like material V-゛ The present invention relates to a method of manufacturing silica aerogel-like materials. Sirikaniaku Gels are porous materials with very low density, containing up to 99% air. To the present invention The microscopic silica aerogel produced by Ru. This material has good thermal insulation properties due to its large porosity, which makes the material It is also transparent because the rod pore diameter is smaller than the wavelength of visible light. silica airgel The typical properties of are as follows.

Density near 0-250kg/z3 Refractive index 1.02-1.05 Thermal conductivity in air: 0, 0 2 1 W/mK at 20°C Thermal conductivity in vacuum : 0.008W/mK at 20℃ Particle size: 4-7nth Cloudy pore diameter・lO~20nm Transmittance 88% at 10i+z thickness Silica airgel has good insulation properties that are almost twice that of asbestos; Since it is also transparent, it can be used to insulate windows. Silica xerogel/ Due to its porosity, airgel also has a very large liquid suction capacity5, making composite As a starting material for materials and also as a carrier for catalysts and liquids, e.g. electrolytes It can also be used as

In order to produce silica airgel, i & Hatsu uses sodium silicate hydrate as a starting material. Aqua gel is produced by the reaction between silicate and water using hydrogen chloride as a catalyst. Agel) was formed. However,5 this manufacturing route requires The aqua gel has to be washed with alcohol, which is very time-consuming. It is something. The drying step preferably removes all liquid and removes the desired silica network. It is necessary to leave only the lick.

Recently, the starting material tositetetramethoxysilane for producing silica airgel , S i (O C H,), , TMOS has also come to be used, T MOS is a suitable starting material because it is easy to handle, easily manufactured in pure form, and easily hydrolyzed. It is a fee. However, it is toxic and expensive. The formation of alcogel is the so-called TMOS can be directly hydrolyzed using acid and/or base as a catalyst using the sol-gel method. This is done by The formed alcogel is surrounded by aqueous methanol The problem that occurs at that time is that the air To remove aqueous methanol from its silica skeleton to obtain logels, silica It is necessary to remove the liquid surrounding the cascade, this is the front part of the liquid When removing the alcogel, the capillary forces acting on the alcogel are removed or at least reduced. This can be done by removing the liquid, or by removing the liquid to prevent the pores from collapsing. Two drying procedures are possible when strengthening the network and also eliminating capillary forces. ) supercritical drying, in which the solvent in the liquid phase is dried at a temperature higher than the critical temperature of that solvent; In an autoclave, it is converted to the gas phase at elevated pressure. Modify this drying method In this method, the solvent is extracted with another compound, such as CO2, which has a lower critical point. Is Rukoto. Supercritical drying means that if there is a leak, a large amount of methane will be expelled. This is a somewhat dangerous method as the ball can cause an explosion.

b) Lyophilization, in which the alcogel is frozen to a solid state, after which the solvent is removed under reduced pressure. to sublimate it.

A third possible method is as follows: C) Air drying and direct evaporation of the solvent, in which case the liquid phase is converted to the gas phase. Drying process 6 sentences which would normally result in pore collapse and gel crack formation due to capillary forces. In order to narrow the pore size distribution and thus reduce the strain difference of the alcogel, DCCA C drying control chemical additive (Drying ConLrol Chemi It has been reported that cal Additive) is added to the sol, and Cracks are thus considerably reduced. However, the resulting silica xerogel is relatively large. For example, it has a density of about 1.4 g/cm. Strictly speaking, a) Only the manufacturing method results in an aerogel. In the other two methods b) and C) may be described as silica, silica gel and silica xerogel, respectively. Gels are obtained, which develop roughly the same properties as silica aerogels.

Drying method a) using supercritical drying provides low density and relatively good optical saga. However, the method is susceptible to high pressures and temperatures during drying. It is a more expensive and dangerous method. In the manufacture of tiles for use as window insulation, Because large amounts of methanol can be ignited, there is considerable danger during operation. Requires autoclaving which can be dangerous. During supercritical drying, as a medium e.g. , CO2 requires extraction of the solvent.

Drying method b) is inexpensive, but due to volume expansion of the solvent during crystallization (i.e. freezing), This tends to result in cracking of the gel during drying.

Drying step C) is usually performed with large shrinkage of the gel due to collapse of the gel structure. Ru. High-density glasses are produced by sintering from these xerogels, which are not particularly reactive. In this case, it becomes a problem to remove the organic residue, namely DCCA.

The object of the present invention is to have a relatively low density (i.e. a density lower than 0.5 g/cm'); Manufactures silica xerogel (aerogel), a material suitable as a thermal insulation material. give you a way to do it.

According to the present invention, tetraalkoxysilane is hydrolyzed and polycondensed to produce an aqueous alkali Forming alcogel, which is a silica skeleton surrounded by coal A new and improved method for producing low-density silica xerogels has been developed. Given. The method involves converting the formed alcogel into tetraalkoxysilane/tetraalkoxysilane. It is characterized by contacting with 8 liquids. Maintain the contact above room temperature to remove the silica. The mixture is stabilized and then slowly heated at temperatures above room temperature and pressures above atmospheric pressure. and dry. Before contacting the alcogel with a solution of tetraalkoxysilane, To clean the gel by contacting the lucogel with a liquid, the water surrounding the lucogel skeleton is removed. (to change the composition of the alcohol), it is appropriate to substitute functional groups on the surface. be. This liquid can be, for example, water and alcohol, preferably about 40% methanol. consisting of a mixture of This liquid may be replaced several times. Add for cleaning The liquid has a temperature up to its boiling point, preferably room temperature.

It is suitable to use tetramethoxysilane for producing alcogels, and Afterwards, the formed gel is placed in a lower alcohol, especially methanol. Contact with a solution of tetraethoxysilane.

Contact between the alcokel and the later added tetraalkoxysilane forms a gel network. Alco Temperatures at which no danger arises for the gel, preferably from 20 to 200°C, especially from 40 to It is suitable to maintain a temperature of 80°C. The longer the aging time, the more the product This results in a maximum of pores j-1, ie, a minimum density. Comparing alcogel to a liquid Washing with hydroalcohol reduces the shrinkage of the gel and enlarges the pores. become.

The alcohol used is usually a 1.2- or trihydric alkanol, especially a 1-! 0 One having a carbon atom of @, preferably methanol.

Drying too quickly will lead to collapse, so it is essential to dry under controlled conditions. Qualitatively important. Controlled drying is due to the presence of fluids surrounding the silica skeleton. Drying in an atmosphere containing components present in the liquid or components formed from the liquid at elevated temperatures. This can be achieved by doing. Drying is carried out by e.g. It may be carried out in two chambers, or the alcogel may be almost completely covered, e.g. You can also do this while keeping it covered up to %, which will give you the same effect. It will be done. Drying is suitably carried out at a temperature in the range 40-200°C. The drying temperature is room The temperature may be gradually changed from the temperature to the boiling point of the aqueous alcohol.

The xerogels thus formed have low densities (e.g., Q, 5 g/cx' or less). (lower) and also have a homogeneous structure.

Example 1 Alcogel was produced by hydrolysis and polycondensation of TMOS. Hydrolysis is , NH, OH as a catalyst, stoichiometric amount of water (TM01:Al ratio, 1.4), and methanol as a solvent. Gel formation was performed at approximately 0°C. a Lucogel is a removable Nescofi/L (Nescofi 1m) bottom The molds were cast into Pi μ Nox/Teflon molds with a After gel formation, completely covered After standing for up to several hours, the mold containing the alcogel was soaked with tetraethoxysilane ( TEOS) and methanol. About 24 hours after bathing the mold was removed and the bath was kept covered for an additional 24 hours. All soaking and subsequent storage The temperature was maintained at approximately 60°C during the period. Next, cover the gel to a degree of 97%, about 6 It was dried at 0° C. and 1 atmosphere pressure. 0.42~0.13g/cy' by drying A monolithic gel was obtained with a density in the range of . Different molar ratios of T in the aging solution EOS and methanol were used. Increasing the amount of TEOS in the aging liquid, this liquid With increasing time in the pores, the density decreases linearly and the nonporous diameter increases correspondingly. Ta. The shrinkage of alcogel during drying is 15-30% depending on the molar ratio and aging time. It was within range. The specific surface area of xerogel is in the range of 600 to 650++2/g. It was. The thermal conductivity of the silica xerogel material formed is 0.024 at 45°C. It was measured that the power was reduced to ±0.004 W/i,K.

Example 2 An alcogel was prepared as described in Example 1.

After leaving it covered for up to several hours, the mold containing the alcogel is poured into methanol and water. (for example, 30% by volume of water). liquid mixture for 24 hours It was replaced three times at regular intervals. The alcogel in the liquid mixture was kept at room temperature during all washes.

After 4 days, the cleaning solution was replaced with a solution of tetraalkoxysilane as in Example 1. I changed it. The rest is the same as in Example 1.

By treating the alcogel with a solution of water and methanol, the alcogel during drying can be The shrinkage of the tube has decreased. The shrinkage of the alcogel during drying was approximately 13%. manufacturing The thermal conductivity of the silica xerogel decreased to 0.028 ± 0.04 W/llK. was measured.

Increasing the amount of water in the liquid mixture used to wash the alcogel increases the surface area. decreased and the pore size increased linearly.

Example 3 Same procedure as in Examples 1 and 2, but in the liquid mixture used during washing and in the gel network. as a solvent for the tetraalkoxysilane used to strengthen the Tanol was replaced by ethanol.

international search report international search report PCT/M) 92700096

Claims (7)

[Claims] 1. By hydrolysis and polycondensation of tetraalkoxysilane, form an alcogel, which is a silica skeleton surrounded by A method for producing silica xerogel (aerogel) by removing coal by evaporation. Then, the formed alcogel is brought into contact with a solution of tetraalkoxysilane. to strengthen the silica skeleton by maintaining the contact above room temperature, and then the gel is heated to room temperature. A silica xeroge that dries slowly at temperatures above room temperature and near atmospheric pressure. manufacturing method. 2. The alcogel is prepared from a solution of a tetraalkoxysilane, preferably an alcoholic solution thereof. The method according to claim 1, wherein the method is contacted with a liquid. 3. Claims wherein the alcogel is optionally washed with aqueous alcohol before further contacting. The method described in 1 or 2. 4. Tetramethoxysilane is used to make alcogel, which is then mixed with alcohol, Claim 1: Contacting with a solution of tetraethoxysilane, in particular in methanol. 3. The method according to any one of 3 to 3. 5. Contact between the alcogel and the tetraalkoxysilane solution is carried out at 20 to 200°C. 5. According to any one of claims 1 to 4, maintained at a temperature ranging from 6 hours to 16 days. Method. 6. 6. A method according to claim 5, wherein the subsequent drying is carried out at a temperature in the range 40-200<0>C. 7. Drying can be caused by components present in the liquid surrounding the silica skeleton or even higher For example, the surface of the gel may be dried during drying in an atmosphere containing components formed from said liquid at a 7. The method according to claim 6, carried out by covering up to 99% of the surface.