CN106430219A - Method for preparing silicon oxide aerogel with low cost - Google Patents

Abstract

The invention relates to a method for preparing silicon oxide aerogel with low cost. Cheap industrial water glass is adopted as a precursor, water is adopted as a reactive solvent, oxalic acid is adopted as an acid catalyst, and the high-temperature-resistant blocky silicon oxide aerogel with excellent performance is prepared through a normal-pressure drying process. The prepared aerogel sample is low in density, high in specific area and good in temperature resistance, and the hydrophobic temperature resistance in air can reach 400 DEG C. The method has the advantages of being simple in preparation process and low in cost, the application range of the aerogel is widened through excellent high-temperature stability of the prepared aerogel, and the aerogel can be widely applied to the field of heat insulation.

Description

A low-cost method for preparing silica airgel

technical field

The invention belongs to the technical field of preparation of inorganic nanoporous materials, and relates to a method for preparing silica airgel at low cost.

Background technique

Airgel is a highly dispersed solid-state material in which colloidal particles or polymer molecules are aggregated into a nanoporous network structure, and the pores are filled with a gaseous dispersion medium. This material with a sponge-like open-pore structure has a very large specific surface area, and the structure of the material can be controlled at the microscopic scale of nanometer scale, so that it has many unique properties. The unique structural characteristics of aerogels make aerogels have singular properties in thermal, electrical, acoustic, optical and other aspects.

The preparation of SiO ₂ airgel is usually carried out by supercritical drying, the molding effect is better, and the nanoporous network structure can be well maintained. However, the equipment required for supercritical drying is expensive, and there is a relatively high risk of high temperature and high pressure. Therefore, the preparation of _SiO2 airgel by atmospheric pressure drying is an inevitable requirement for large-scale production and application. At present, the silicon sources used in the synthesis of silica airgel include orthosilicates, polysiloxanes, silica sol, water glass, and rice husk or fly ash. The use of orthosilicates and polysiloxanes as silicon sources has problems such as high price, high cost, and strong toxicity. Although rice husk or fly ash is cheap, the preparation process is complicated, and the performance of the prepared airgel is relatively low. Difference.

Patent CN1126591C (ZL97181105.9) discloses a method for organically modifying airgel. The method for removing salt in water glass is to first adjust the water glass solution to pH under the action of acidic ion exchange resin, inorganic acid or hydrochloric acid. <3, the gel is obtained by adding a basic catalyst to silicic acid, and then the gel is washed with deionized water to free all the electrolytes in it. Chinese patents CN201210121968.0 and CN201210114691.9 use sodium silicate as a raw material and are prepared by a two-step sol-gel method. After ion exchange, they are aged with an ethanol solution of tetraethyl orthosilicate, and finally undergo solvent exchange and modification. The airgel is obtained by drying, and the tetraethyl orthosilicate used greatly increases the preparation cost, and the density of the obtained airgel is also relatively high. Ni Xingyuan et al. (Chinese Patent, Application No. 200810042222.4) disclosed a method for preparing hydrophobic silica aerogels under normal pressure by using straw ash as a raw material, through solvent replacement and surface modification, but the process is relatively complicated. At present, most processes remove salt through cation exchange, but strong acid cation exchange resin is used to remove sodium ions and other metal ions in water glass. Due to the limited capacity of the cation exchange resin (generally 5 mmol/g), the experimental level of this method is acceptable. If it is industrialized production, the high concentration of sodium ions in the water glass will cause the exchange capacity of the ion exchange resin to quickly saturate, and continuous production cannot be achieved at all. At present, there are many research reports on the preparation of silica airgel by atmospheric drying, but there are certain defects, such as high cost, complicated process, and the prepared airgel has a small specific surface area and poor temperature resistance, which restricts the Industrial applications of airgel. Therefore, there is an urgent need to study silica aerogels with simple preparation process and low cost.

Contents of the invention

The present invention aims at the above-mentioned problems of the prior art, and provides a low-cost method for preparing silica airgel.

In order to achieve the above-mentioned purpose of the invention, the technical solution adopted in the present invention is: a method for preparing silicon oxide aerogel at low cost, which is prepared according to the following steps:

Step 1: Dilute the industrial water glass with deionized water to obtain a water glass solution, and ultrasonically treat it for a certain period of time after filtration;

Step 2: Take a certain volume of water glass solution, add a certain amount of dry chemical control agent to it, stir for 2-10 minutes, add a certain concentration of oxalic acid until it gels;

Step 3: Aging the wet gel in an organic reagent at a certain temperature for a period of time;

Step 4: After aging, replace the wet gel in a non-polar solvent;

Step 5: placing the replaced wet gel in a mixture of siloxane solvent and non-polar solvent for surface modification;

Step 6: The wet gel modified in Step 5 is washed with a non-polar solvent and then dried under normal pressure to obtain a transparent massive silica airgel.

The volume ratio of the silicon source to deionized water in step 1 is preferably 1:2~1:10, the modulus of the silicon source is industrial water glass of 3~3.5, and the ultrasonic treatment time is 0~10min.

In step 2, the volume of water glass is 10-50ml, and the dry chemical control agent is one of formamide, N,N-dimethylformamide, polyethylene glycol, glycerol, oxalic acid, and its molar ratio to Si 0~1:1, the concentration of oxalic acid is 0~2mol/L.

In step 3, the organic solvent is one of methanol, ethanol, isopropanol, and butanol, the aging temperature is 30-70° C., and the aging time is 0-5 days.

The non-polar solvent described in step 4 is preferably one of n-hexane, cyclohexane and n-heptane.

The siloxane solvent described in step 5 is preferably one of trimethylchlorosilane, hexamethyldisilazane, hexamethyldisiloxane, 3-aminopropyltriethoxysilane, silane The volume ratio of the coupling agent to the wet gel is 0.05-0.5, and the non-polar solvent is preferably one of n-hexane, cyclohexane, and n-heptane.

The non-polar solvent described in step 6 is preferably one of n-hexane, cyclohexane, and n-heptane, the drying temperature under normal pressure is 30-200° C., and the drying time is 5-15 hours.

The invention discloses a low-cost method for preparing silicon oxide aerogels. Low-density silicon oxide airgel is prepared by using cheap industrial water glass as a silicon source, adding oxalic acid, one-step reaction, and drying under normal pressure. In the silica airgel, the silica airgel is prepared by ultrasonic treatment and drying under normal pressure with the addition of a drying chemical control agent. The sample has the characteristics of low density, uniform pore structure, etc., and the hydrophobic temperature resistance reaches 400°C.

Description of drawings:

Accompanying drawing 1 is the macrophotograph of the silica airgel prepared by the present invention.

detailed description

Example 1

Take 20ml of industrial water glass with a modulus of 3.2 according to the volume ratio of industrial water glass and water 1:4, mix 80ml of deionized water in a beaker, stir for 10min, then filter and ultrasonicate for 5min, add 0.47ml to the solution Glycerol, stir for 3 minutes, add 8.4ml of 1mol/L oxalic acid solution, stir for 1 minute, wait for it to completely gel, add deionized water, then place it in a 40°C water bath for two days, and then replace it with ethanol for one day, Then, the wet gel was replaced in n-hexane, and the wet gel was modified in a mixture of trimethylchlorosilane and n-hexane for 10 h in a water bath at 40°C. The fully modified gel floats on the modified liquid product as a whole, then is replaced by n-hexane for 24 hours, and finally dried at 40°C, 60°C, 80°C, and 100°C for two hours each to obtain an airgel sample.

The obtained airgel sample has a density of 0.068g/cm ³ and a specific surface area of 699.8m ² /g.

Example 2

Measure 20ml of industrial water glass with a modulus of 3.2 according to the volume ratio of industrial water glass and water 1:4, mix 80ml of deionized water in a beaker, stir for 10min, then filter and ultrasonicate for 10min, add 0.47ml to the solution Glycerol, stir for 3 minutes, add 8.7ml of 1mol/L oxalic acid solution, stir for 1 minute, wait until it is completely gelled, add deionized water, then put it in a 40°C water bath for two days, and then replace it with ethanol for one day, Then, the wet gel was replaced in n-hexane, and the wet gel was modified in a mixture of trimethylchlorosilane and n-hexane for 10 h in a water bath at 40°C. The fully modified gel floats on the modified liquid product as a whole, then is replaced by n-hexane for 24 hours, and finally dried at 40°C, 60°C, 80°C, and 100°C for two hours each to obtain an airgel sample.

The obtained airgel sample had a density of 0.070 g/cm ³ and a specific surface area of 607.7 m ² /g.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments, and those skilled in the art can also make various equivalent modifications or replacements without departing from the spirit of the present invention. , these equivalent modifications or replacements are all included within the scope defined by the claims of the present application.

Claims (7)

1. a kind of low cost prepares the method for silica aerogel it is characterised in that being prepared in the steps below：

Step one：Industrial waterglass is added deionized water dilution to obtain water glass solution, supersound process certain time after filtration；

Step 2：Take above-mentioned water glass solution, be added thereto to a certain amount of dry chemistry controlling agent, after stirring 2 ~ 10min, add finite concentration oxalic acid and treat its gel；

Step 3：Wet gel is placed at a certain temperature in organic reagent aging a period of time；

Step 4：After aging, wet gel is placed in displacement in non-polar solven；

Step 5：Wet gel after displacement is placed in the mixed liquor that siloxane solvent is with non-polar solven and carries out surface modification；

Step 6：By the wet gel after modification in step 5 after non-polar solven washing, constant pressure and dry can get transparent cake silica aerogel.

2. low cost according to claim 1 prepare silica aerogel method it is characterised in that in described step one silicon source and the ratio of the volume of deionized water be preferably 1:2~1:10, the modulus of described silicon source is 3 ~ 3.5 industrial waterglass, and sonication treatment time is 0 ~ 10min.

3. the method that low cost according to claim 1 prepares silica aerogel, it is characterized in that, in described step 2, water glass solution volume is 5 ~ 30ml, dry chemistry controlling agent is Methanamide, N, one of dinethylformamide, Polyethylene Glycol, glycerol, oxalic acid, it is 0 ~ 1 with the mol ratio of Si:1, the concentration of oxalic acid is 0 ~ 2mol/L.

4. low cost according to claim 1 prepare silica aerogel method it is characterised in that in described step 3 organic solvent be one of methanol, ethanol, isopropanol, butanol, aging temperature be 30 ~ 70 DEG C, the time be 0 ~ 5d.

5. low cost according to claim 1 prepares the method for silica aerogel it is characterised in that non-polar solven described in described step 4 is preferably one of normal hexane, hexamethylene, normal heptane.

6. the method that low cost according to claim 1 prepares silica aerogel, it is characterized in that, siloxane solvent described in described step 5 is preferably one of trim,ethylchlorosilane, hexamethyldisiloxane, hexamethyldisiloxane, APTES, silane coupler is 0.05 ~ 0.5 with the ratio of the volume of wet gel, and described non-polar solven is preferably one of normal hexane, hexamethylene, normal heptane.

7. low cost according to claim 1 prepare silica aerogel method it is characterised in that in described step 6 non-polar solven be preferably one of normal hexane, hexamethylene, normal heptane, constant pressure and dry temperature be 30 ~ 200 DEG C, drying time be 5 ~ 15h.