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Process for preparing hydrophobic silicon dioxide aerogel using rice husk ash as raw material

A technology of silicon dioxide and rice husk ash, applied in the directions of silicon dioxide, silicon oxide, chemical instruments and methods, can solve the problems of high density, high cost of raw materials, small pore size, etc., and achieves simple process, reduced production cost, Easy to operate effect

Inactive Publication Date: 2006-01-25
TSINGHUA UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, there are problems of expensive raw materials and high cost, which directly affects the large-scale production and application of aerogels.
[0007] In the inventor's previous Chinese patent (application number 03127920.1, publication number CN1449997A), the use of rice husk ash after burning agricultural waste rice husk as a silicon source was introduced to produce silicon aerosol by sol-gel and supercritical drying The glue method, although the cost has been greatly reduced, but the prepared product still has the problem of hydrophilicity
[0008] The method proposed in another Chinese patent (Application No. 200510011378.2) of the present inventor also utilizes rice husk ash as a silicon source to dry and prepare silica airgel under normal pressure conditions, but the prepared product still exists Hydrophilicity problem, and compared with products prepared by supercritical drying method, there are problems of small pore volume, high density and small pore size

Method used

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Examples

Experimental program
Comparison scheme
Effect test

preparation example Construction

[0035] (1) Preparation of hydrosol: Add rice husk ash to a strong alkali solution with a concentration of 0.1 to 1.0 mol / L, the ratio of the alkali solution to rice husk ash is 20 to 50:1 (L / kg), under normal pressure Leach for 5 to 120 minutes in boiling state;

[0036] (2) Filtration and acid treatment process: titrate and neutralize the filtrate after filtering the leaching solution with 0.1-1.0 mol / L inorganic strong acid to a pH value of 5-9, and then stand still to produce silica hydrogel;

[0037] (3) Aging: Aging the hydrogel prepared in (2) above at a temperature between 15°C and 60°C for 1 minute to 48 hours;

[0038] (4) washing with water, washing the gel obtained in the above (3) with deionized water for 1 to 5 times, and the volume ratio of deionized water to the gel is 1 to 5: 1;

[0039] (5) Organic solvent replacement, using an organic solvent to replace the water in the hydrogel prepared in (4) above, the replacement time is 1.5 to 6 hours, and the volume ra...

example 1

[0048] Mix 10 grams of rice husk ash with 300 milliliters of 0.9 mol / L NaOH solution, boil at normal pressure for 90 minutes, filter the filtrate obtained, neutralize it to pH 7 with 1 mol / L sulfuric acid; leave it to form water gel; the obtained hydrogel was aged at 25°C for 48 hours, washed 3 times with water; then the hydrogel was soaked in ethanol for 4 hours, and then white silica airgel was prepared by supercritical drying method, which was Put it in a steam bath of hexamethyldisilazane for 1 hour (30° C.), and take it out to obtain a hydrophobic silica airgel. To measure the hydrophobicity, put the prepared airgel directly into the water, weigh it after 10 days, and find that there is no adsorbed water at all; measure the hydrophobicity with methanol aqueous solution, and the index can reach 40%. Its specific surface area is 460.7m 2 / g, the pore volume is 3.3cm 3 / g, the apparent density is 39.8kg / m 3 , The average pore diameter of the internal micropores is 33 nano...

example 2

[0050] Mix 15 grams of rice husk ash with 500 milliliters of 0.1mol / L NaOH solution, boil at normal pressure for 120 minutes, filter the filtrate obtained, neutralize it to pH 8 with 1mol / L hydrochloric acid; let stand to form water Gel; the obtained hydrogel was aged at 27°C for 35 hours, and then washed 4 times with deionized water; then soaked in methanol for 6 hours, and then dried with supercritical carbon dioxide fluid to obtain white carbon dioxide Silica airgel, put it in a steam bath of dimethyldimethoxysilane, and get hydrophobic silica airgel within 12 hours (26°C). To measure the hydrophobicity, put the product directly on the water surface, and after 15 days, it is weighed to find that there is no adsorbed water at all; the hydrophobicity is measured by the method of methanol aqueous solution, and the index can reach 15%. Its specific surface area is 417.7m 2 / g, the apparent density is 40.7kg / m 3 , the pore volume is 2.5cm 3 / g, the average pore diameter of th...

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Abstract

A process for preparing the hydrophobic SiO2 aero-gel from rice husk ash includes such steps as burning rice husk to obtain its ash, extracting its hydro-gel in inorganic strong-alkaline aqueous solution, neutralizing by inorganic strong acid, laying aside to generate SiO2 hydro-gel, filter, acid treating, ageing, water washing, displacing the water from the hydro-gel by organic solvent, supercritical drying and modifying surface. Its advantages are high specific surface area and pore volume, and low apparent density.

Description

technical field [0001] The invention discloses a method for preparing hydrophobic silica airgel by using rice husk ash as a raw material, relates to a preparation method of hydrophobic silica airgel, and belongs to the technical scope of chemical material preparation. Background technique [0002] Silica airgel is a porous amorphous solid material containing a large amount of air, low density, and high porosity. Its porosity can reach more than 90%, and the typical pore size is in the range of 1-100nm. Silica aerogels show unique properties in many aspects such as mechanics, acoustics, thermals, optics, etc. They are obviously different from porous materials with pore structures on the order of microns and millimeters, and their fine nanostructures make the thermal conductivity of materials The efficiency is extremely low, with a large specific surface area, and the scattering of light and sound is much smaller than that of traditional porous materials. Therefore, silica ae...

Claims

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Application Information

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IPC IPC(8): C01B33/14C01B33/158
Inventor 王涛李婷
Owner TSINGHUA UNIV
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