WO2020082782A1 - 一种二氧化硅气凝胶制备方法及应用该方法制备的气凝胶 - Google Patents

一种二氧化硅气凝胶制备方法及应用该方法制备的气凝胶 Download PDF

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WO2020082782A1
WO2020082782A1 PCT/CN2019/094908 CN2019094908W WO2020082782A1 WO 2020082782 A1 WO2020082782 A1 WO 2020082782A1 CN 2019094908 W CN2019094908 W CN 2019094908W WO 2020082782 A1 WO2020082782 A1 WO 2020082782A1
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drying
reaction
aerogel
raw material
precursor
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PCT/CN2019/094908
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English (en)
French (fr)
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孙晔
李振声
胡友双
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天津摩根坤德高新科技发展有限公司
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Priority claimed from CN201811232214.6A external-priority patent/CN109351292A/zh
Priority claimed from CN201811417970.6A external-priority patent/CN109399653A/zh
Priority claimed from CN201910148217.XA external-priority patent/CN109721059B/zh
Priority claimed from CN201910144294.8A external-priority patent/CN109650397A/zh
Application filed by 天津摩根坤德高新科技发展有限公司 filed Critical 天津摩根坤德高新科技发展有限公司
Publication of WO2020082782A1 publication Critical patent/WO2020082782A1/zh
Priority to US17/238,187 priority Critical patent/US12017921B2/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
    • C01B33/157—After-treatment of gels
    • C01B33/158—Purification; Drying; Dehydrating
    • C01B33/1585—Dehydration into aerogels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/0091—Preparation of aerogels, e.g. xerogels
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
    • C01B33/141—Preparation of hydrosols or aqueous dispersions
    • C01B33/142—Preparation of hydrosols or aqueous dispersions by acidic treatment of silicates
    • C01B33/143—Preparation of hydrosols or aqueous dispersions by acidic treatment of silicates of aqueous solutions of silicates
    • C01B33/1435—Preparation of hydrosols or aqueous dispersions by acidic treatment of silicates of aqueous solutions of silicates using ion exchangers
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
    • C01B33/157—After-treatment of gels
    • C01B33/158—Purification; Drying; Dehydrating
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
    • C01B33/157—After-treatment of gels
    • C01B33/159—Coating or hydrophobisation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/32—Thermal properties
    • C01P2006/37—Stability against thermal decomposition

Definitions

  • the invention belongs to the field of aerogel preparation, and particularly relates to a method for preparing silica aerogel and aerogel prepared by the method.
  • Aerogel usually means that the liquid in the hydrogel structure is discharged by a certain method, and the nanometer pore size is not destroyed.
  • the porous medium with a three-dimensional network structure has special characteristics such as small density, huge specific surface area, and nanometer pore size.
  • Silica aerogel is a common aerogel.
  • SiO2 aerogel is a kind of lightweight nanoporous amorphous solid material with excellent thermal and thermal insulation properties. It has high porosity, large specific surface area, low density and low thermal conductivity at room temperature. It is precisely because of these characteristics that aerogel materials have broad application potential in thermal, acoustic, optical, microelectronics, and particle detection.
  • the preparation of aerogel usually consists of sol-gel process and supercritical drying treatment. In the sol-gel process, by controlling the hydrolysis and polycondensation reaction conditions of the solution, nano-clusters of different structures are formed in the solution, and the clusters adhere to each other to form a gel body, and around the solid skeleton of the gel body.
  • aerogel Full of liquid reagents remaining after chemical reaction.
  • the formation mechanism of aerogel is to not only dehydrate the gel formed in the early stage during the drying process, but also ensure that the gel does not collapse, so that the air enters the gel network to replace the original water in the gel.
  • a method for preparing aerogel using a supercritical drying process generally uses methyl orthosilicate and ethyl orthosilicate as a silicon source to prepare a silica aerogel.
  • These organic silicon sources require hydrolysis to produce silicic acid, a large amount of volatile organic compounds are generated during the hydrolysis process, and a large amount of volatile organic waste gas is emitted during the mixing and drying process.
  • sodium silicate solution as the silicon source.
  • Sodium silicate is used as a raw material in large quantities, resulting in excessive sodium ions passing through the intermediate product. If excessive sodium ions enter the final product, it will cause the product It is corrosive to metals.
  • sodium ions need to be removed.
  • the sodium ion cleaning process usually generates a large amount of wastewater.
  • dimethylchlorosilane is also mainly selected as the precursor raw material.
  • the hydrolysis of this raw material itself will generate a large amount of chloride ions.
  • the chloride ions are also highly corrosive. If excessive chloride ions remain in the product Will affect product quality.
  • a large amount of liquid needs to be used for cleaning, thus generating a large amount of chlorine-containing waste liquid.
  • Silicon source A substance that can provide silicon for the production of silica aerogel.
  • Solid silicon source can be white carbon black, silicon fine powder, diatomaceous earth solid silicon-containing compound, or a mixture of the above materials. It has a large reaction contact surface and can form silicate ions under the action of alkali ions.
  • Alkaline solution The alkaline solution referred to in this article includes alkaline aqueous solution (such as sodium hydroxide solution, sodium silicate solution), alkaline organic solution (such as sodium ethoxide solution in ethanol), and the above two solutions. mixture.
  • alkaline aqueous solution such as sodium hydroxide solution, sodium silicate solution
  • alkaline organic solution such as sodium ethoxide solution in ethanol
  • the preparation method of silica aerogel using organic silicon sources will use a large amount of organic substances, such as mixing, stirring and drying materials. A large amount of organic waste gas will be generated in the process.
  • organic silicon sources such as methyl orthosilicate and ethyl orthosilicate
  • sodium silicate solution sodium silicate is used as a raw material in large quantities, resulting in excessive sodium ions passing through the intermediate product. If the excessive sodium ions enter the final product, the product will cause corrosion to the metal In order to ensure product quality, sodium ions need to be removed.
  • the sodium ion cleaning process usually generates a large amount of wastewater. The problem of large amount of waste water also appears in the preparation process of silica aerogel using other silicates as the silicon source.
  • this technical solution uses a solid silicon source as a raw material for providing silicon element, which is mixed with an alkaline solution under certain conditions, and the aerogel precursor is obtained after mixing After the reaction of the precursor and the precursor gel, the aerogel product is prepared after drying, the steps are as follows:
  • the solid silicon source is mixed with the alkaline solution under certain conditions, and the aerogel precursor is obtained after mixing.
  • the precursor is dried to obtain an aerogel product.
  • the solid silicon source can form silicate ions under the action of alkali ions.
  • the silicate ions are extremely unstable. When encountering hydrogen ions, they quickly combine into silicic acid. Under certain conditions, the silicic acid undergoes a gel reaction to form a gel.
  • This technical solution can provide a very large reaction contact surface due to the use of a solid silicon source, increase the chance of capturing alkali ions, and accelerate the formation of silicate ions; at the same time, the porous medium is a multi-molecular aggregate, which has a large adsorption capacity and forms silicon Acid ions are easily captured by the porous medium and adsorbed on the surface of the porous medium.
  • the gel reaction is mainly an interfacial reaction, such as a gel reaction occurring at the solid-liquid interface.
  • a method of obtaining silica aerogel by drying can be used. That is, a part of the porous silica solid medium participates in the reaction as a reactant, and a part as a seed to adsorb newly generated silica.
  • a porous medium with a large pore size forms a hydrogel with a small pore size.
  • this technical solution avoids excessive sodium ion in the product due to the use of solid silicon source as the silicon source The risk is that there is no need for sodium ion cleaning, and a large amount of sodium-containing wastewater is avoided.
  • the reaction rate can be controlled by controlling the solid-liquid ratio, so the specific surface area of the product can be increased and the thermal conductivity can be reduced under the premise of optimized control. Overall improve product quality.
  • Plan B is an improvement of the basic technical plan A.
  • other raw materials include silicon phosphate, sodium silicate and water.
  • the steps of scenario B are as follows:
  • the precursor is dried to obtain an aerogel product.
  • the silicon phosphate in Scheme B can be replaced with silicon polyphosphate, or a mixture of silicon phosphate and silicon polyphosphate.
  • the main reason for the reduction of waste solution in scheme B is that the solid silicon source sodium silicate reacts with the aqueous solution of silicon phosphate, and the desired product silicic acid will be generated.
  • Silicon phosphate reacts with water to hydrolyze to generate phosphoric acid and silicic acid.
  • Phosphoric acid can generate hydrogen ions in water.
  • Hydrogen ions and silicate ions in the solution can also generate product silicic acid.
  • white carbon black and silicon fine powder of solid silicon source One or both of white carbon black and silicon fine powder of solid silicon source. Both white carbon black and silicon fine powder mainly contain silicon dioxide and are of porous structure. White carbon black and silicon fine powder react with sodium ions to form silicon Sodium and sodium silicate continue to hydrolyze to obtain silicic acid. After drying the precursor, the silicic acid shrinks to form silica, and at the same time, silica and silica powder as the gel core particles adsorb the silica obtained after shrinkage, thereby forming a porous silica aerogel, the process Avoid the generation of waste liquid.
  • the mass ratio of silicon phosphate to sodium silicate is 1-100: 100; the weight ratio of gel core particles to sodium silicate is 1-50: 100.
  • the mass ratio of silicon phosphate to sodium silicate is 5-50: 100.
  • the mass ratio of silicon phosphate to sodium silicate is 10-30: 100.
  • the silica gel made of silicon phosphate and sodium silicate in this ratio range has a larger specific surface area and a smaller thermal conductivity.
  • the weight ratio of gel core particles to sodium silicate is 5-20: 100.
  • the ratio of gel core particles to silica gel prepared by sodium silicate has a larger specific surface area and thermal conductivity. smaller.
  • the silica aerogel can be obtained by atomization drying or natural drying.
  • the powdery silica aerogel is obtained by atomization drying, and the drying temperature can be selected from 200 to 500 ° C. Drying within this temperature range can obtain a silica aerogel of good quality.
  • the precursor to the solid surface for natural drying during use, and the initial gel is 40 to 50 hours at room temperature, and the final drying time is 6 to 7 days.
  • silica aerogel It is prepared by the above-mentioned method for preparing silica aerogel, and the prepared silica aerogel has a porous structure. This structural feature makes the silica aerogel have a larger specific surface area and a smaller thermal conductivity.
  • Scheme C is an improved scheme of the basic technical scheme A.
  • other raw materials include an acidic regulator and a low-boiling organic solvent.
  • the steps of scenario C are as follows:
  • the alkaline silicate aqueous solution is reacted with the solid silicon source under the condition of 35 ⁇ 100 °C.
  • the silicate includes but is not limited to sodium silicate, potassium silicate, lithium silicate and other related metal silicates .
  • the acidic substance includes any one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, citric acid, and benzoic acid.
  • the low boiling point organic solvent includes any one of ethanol, pentane, methylene chloride, or methanol.
  • scheme C can reduce waste liquid.
  • the solid silicon source reacts in the alkaline silicate solution, and the desired product silicic acid is generated, and the silicate is the role of the catalyst at this time.
  • a large amount of silicate particles still exist in the alkaline solution, and then acidic substances are added thereto, and the hydrogen ions provided by the acidic substances combine with the silicate ions to generate the desired silicic acid.
  • Scheme C reduces the use of sodium silicate solution, thereby reducing the use of sodium ions in subsequent cleaning liquids, thereby reducing To produce waste liquid.
  • the alkaline silicic acid solution is reacted with the solid silicon source under the condition of 35 ⁇ 100 °C, after cooling to room temperature, the acidic substance is added to adjust the pH value to 6.5 ⁇ 7.5, and the reaction obtains the precursor; Includes silicic acid or silicate.
  • the silicate may be sodium silicate, potassium silicate, calcium silicate, or the like.
  • the silicate solution is an aqueous solution of silicate, and the silicate is hydrolyzed in water to make the solution alkaline.
  • the silicic acid solution is obtained by dissolving silicic acid in the acid solution.
  • the silicic acid solution is an alkaline solution.
  • the pH value of the silicic acid solution is 10-14.
  • the source of silica dissolves and reacts to form silicic acid at a temperature of 35-100 ° C under alkaline conditions. After cooling to room temperature, an acidic substance is added, and the acidic substance provides hydrogen ions, and the hydrogen ions replace the salt ions of the silicic acid substance to generate silicic acid, and then a precursor is obtained.
  • the solvent is replaced with a low-boiling organic solvent to replace the water in the precursor, and then dried to make the organic solvent volatilize to retain the porous structure in the precursor, thereby obtaining a high void ratio and a specific ratio Silica aerogel with large surface area.
  • the drying method is microwave drying. After the microwave enters the gel and is absorbed, its energy is converted into heat energy inside the material dielectric.
  • the heat conduction direction of microwave drying is the same as the diffusion direction of the organic solvent, the heat can penetrate uniformly, and has a drying rate Large, even drying effect.
  • the silica source includes one or more of white carbon black and silicon fine powder.
  • the main components of silica and silicon fine powder are both silica and both have a porous structure.
  • the particle size of white carbon black and silicon micropowder is nanometer level, and it dissolves and reacts to form silicic acid under the temperature of 35 ⁇ 100 °C and alkaline conditions.
  • the reaction temperature of the silicic acid solution and the silica source is 50-90 ° C.
  • the silicic acid solution reacts with silica in this temperature range, and the silica source can dissolve and completely react to generate silicic acid.
  • the acidic substance includes an organic acid and / or an inorganic acid. That is to say, the acidic substance may be an organic acid, an inorganic acid, or a mixture of an organic acid and an inorganic acid.
  • the inorganic acid includes any one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid.
  • the organic acid includes any one of acetic acid, citric acid, and benzoic acid.
  • the low-boiling organic solvent includes any one of ethanol, pentane, dichloromethane, or methanol.
  • the low-boiling organic solvent has a low boiling point, and when drying, the low-boiling organic solvent can be removed even at a low temperature, thereby achieving a better drying effect.
  • silica aerogel prepared by the above method for preparing silica aerogel by using acidic substance modified silicic acid substance.
  • the aerogel prepared by this method has a porous structure. Larger specific surface area and smaller thermal conductivity.
  • Scheme D is an improvement of the basic technical scheme A.
  • sodium silicate and organic esters can also be added to the raw material for modification to produce modified sodium silicate aerogel.
  • the steps of scenario D are as follows:
  • the mixture of sodium silicate and solid silicon source is hydrolyzed with an organic ester to obtain a precursor.
  • the precursor is dried to obtain an aerogel product.
  • the sodium silicate in Scheme D can also be replaced with silica sol.
  • the main reason for the reduction of waste solution in Scheme D is that, first, the solid silicon source reacts in an alkaline silicate solution, which will generate the desired product silicic acid.
  • the sodium silicate reacts with water to hydrolyze to generate silicic acid and provide hydroxide ions , Mainly play a catalytic effect on the reaction.
  • the acid generated in the organic ester hydrolysis reaction can generate hydrogen ions in water.
  • a large amount of silicate particles still exist in the solution.
  • Hydrogen ions and silicate ions in the solution can also generate the desired product silicic acid.
  • the acid produced by the hydrolysis of organic esters can effectively control the gelation speed, and the hydrolysis rate can be controlled by adjusting the acidity and alkalinity.
  • the quality of the products obtained can be controlled, and aerogels of different qualities can be produced as needed.
  • organic ester hydrolysis provides the characteristics of alcohol.
  • the alcohol produced by the hydrolysis of organic esters can replace solvents to replace low-boiling organic solvents such as ethanol.
  • the raw materials are simple and the process is simple.
  • the process simplification becomes a one-step method, replacing the traditional two-step process of replacing the liquid in the gel with an organic solvent, thereby reducing the process, reducing the production cycle, improving the production efficiency, and reducing the production cost.
  • Method The product is gelled at normal temperature and dried under normal pressure when preparing the product, and the process is simple.
  • the method is as follows: a mixture of silicate and solid silicon source and hydrolyzed organic ester are used to obtain a precursor, and the precursor is dried to obtain a silica aerogel.
  • the silicate may be sodium silicate, potassium silicate, calcium silicate, etc.
  • the preferred silicate is sodium silicate.
  • Organic esters are used for modification, and the speed of organic ester hydrolysis can be adjusted by concentration, temperature, acidity and alkalinity.
  • an acid-base indicator such as ammonium triacetate is added to adjust the acidity and alkalinity.
  • a template guiding agent such as alkylbenzenesulfonic acid (or metal salt) can be added, and / or a template agent such as polyvinyl alcohol.
  • the total mass fraction of the template guiding agent and the guiding agent in the system of organic ester hydrolysis reaction is 0 ⁇ 20%.
  • the acid generated in the organic ester hydrolysis reaction can effectively control the gel speed, thereby controlling the specific surface area, pore size and structure of the product.
  • the quality of the resulting product can be controlled, and different qualities can be produced according to needs Aerogel.
  • Alcohol produced by the hydrolysis of organic esters can replace low-boiling organic solvents such as ethanol in solvent replacement.
  • the raw materials are simple and the process is simple.
  • the organic ester may be any organic ester that can be hydrolyzed.
  • Organic esters include, for example and without limitation, at least one of the following types of esters: for example, at least one of silicone esters and organic acid esters divided according to the type of ester group.
  • the above-mentioned silicone esters and organic acid esters may be, for example but not limited to, at least one of conventional esters whose R group contains only a carbon chain structure and aromatic esters whose R group contains an aryl group, and the like.
  • the organic acid ester in the present invention refers to the conventional esters formed by condensation of a carboxyl group and a "-C-OH" alcohol hydroxyl group to form an ester group, such as being divided into a monobasic acid ester and a dibasic acid ester according to the "member" number of the carboxylic acid part And other polyacrylates.
  • the organic ester is a low-molecular-weight liquid ester.
  • the above-mentioned low-molecular-weight means that the organic ester can be in a liquid state at normal temperature and pressure, which facilitates the operation of the hydrolysis reaction.
  • High-molecular-weight esters are generally solid, making the preparation cumbersome and complicated.
  • the organic ester is preferably selected from at least one of silicone ester, monobasic acid ester, and dibasic acid ester.
  • silicone ester for example, but not limited to the following, optionally including ethyl acetate, methyl acetate, ethyl formate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, trimethyl acetate Silylmethyl ester, trimethylsilyl bromoacetate, trimethylsilyl methacrylate, trimethylsilyl isobutyrate, trimethylsilyl propionate, trimethylsilyl isothiocyanate At least one of esters and the like.
  • Template directing agents such as alkylbenzenesulfonic acid (or metal salts) act as wetting agents, increasing the chance of surface contact.
  • Silica particles become a carrier for local reactions and a gel carrier.
  • the polyhydroxy group of polyvinyl alcohol acts as a template and guides silicic acid to form a ring-shaped three-dimensional structure.
  • the white carbon black is hydrophilic and / or hydrophobic white carbon.
  • hydrophobic white carbon can be used, or a mixture of hydrophobic white carbon and hydrophilic white carbon can be used, or only hydrophilic white carbon can be used.
  • Black when hydrophilic white carbon black is added, especially in the case of more hydrophilic white carbon black, silicone hydrophobic agent can be added to achieve the purpose of hydrophobicity, so that the white carbon black can be dissolved in organic ester, so as to achieve the particles Arranged to generate porous media, the gelation effect is better.
  • the mass ratio of sodium silicate to white carbon black is 18-38: 40-60.
  • the mass ratio of white carbon black to organic ester is 40-60: 90-110.
  • the mass ratio of white carbon black to water in the hydrolysis reaction is 40-60: 90-110.
  • the mass ratio of sodium silicate, white carbon black, organic ester, and water in the hydrolysis reaction is 18-38: 40-60: 90-110: 90-110 in order. It is preferably 23-33: 45-55: 95-105: 95-105 in order. More preferably, they are 28: 50: 100: 100 in order.
  • the hydrolysis reaction is continued with stirring under closed conditions, the reaction temperature is 50-70 ° C, and the reaction time is 3-5h.
  • the hydrolysis reaction is carried out in a closed container to prevent volatilization of organic matter.
  • the reaction temperature is optionally any one of 50 °C, 52 °C, 54 °C, 56 °C, 58 °C, 60 °C, 62 °C, 64 °C, 66 °C, 68 °C, 70 °C or any two Range
  • the reaction time is optionally any one of 3h, 3.5h, 4h, 4.5h, 5h or a range between any two, and the hydrolysis effect is better.
  • microwave drying is used for drying, the drying temperature is 160-200 ° C., the drying time is 40-80 min, and the moisture content of the product after drying is less than 0.01%.
  • the drying temperature is optionally 160 ° C, 165 ° C, 170 ° C, 175 ° C, 180 ° C, 185 ° C, 190 ° C, 195 ° C, 200 ° C, or a range between any two, and the drying time is optional
  • the ground is any one of 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min, 80min or the range between any two, to ensure sufficient drying, so that the dried product has a better porous structure.
  • the silicon source includes, but is not limited to, sodium silicate, potassium silicate, lithium silicate and other related inorganic silicate raw materials, including water and cation exchange Resin.
  • the process includes:
  • the precursor is dried to obtain silica aerogel.
  • One of the silicates may be sodium silicate, potassium silicate, calcium silicate, etc.
  • the preferred silicate is sodium silicate.
  • a cation exchange resin is used to perform an ion exchange reaction with a sodium silicate solution.
  • the ion exchange resin absorbs sodium ions in the sodium silicate solution and releases hydrogen ions into the solution.
  • the released hydrogen ions replace the sodium ions of the sodium silicate to generate silicic acid.
  • the cation exchange resin removes sodium ions and promotes gelation, reduces the generation of waste liquid, and is environmentally friendly.
  • the use of ionic resin to shield sodium ions or metal ions can reduce the subsequent steps of removing cations, reduce waste liquid generation, and ultimately improve product quality and reduce the possibility of corrosion of metal materials by products.
  • the basic scheme E reduces the use of sodium silicate solution, thereby reducing the use of liquid in the subsequent cleaning of sodium ions, thereby Reduce the generation of waste liquid.
  • the concentration of the sodium silicate solution is from 0 to saturation, optionally not exceeding 4.5 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / Any one of L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or a range between the two.
  • the mass ratio of sodium silicate to cation exchange resin powder in sodium silicate solution does not exceed 100, for example, the mass of sodium silicate is 1 times, 10 times, 20 times, 30 times, 40 times, 50 times, Any one of 60 times, 70 times, 80 times, 90 times, 100 times, or a range between the two.
  • the ion exchange reaction is carried out under stirring conditions, the reaction temperature is 25-90 ° C, and the reaction time is 1.5-2.5h.
  • the reaction temperature is optionally 25 ° C, 30 ° C, 35 ° C, 40 ° C, 45 ° C, 50 ° C, 55 ° C, 60 ° C, 65 ° C, 70 ° C, 75 ° C , 80 °C, 85 °C, 90 °C, 95 °C, or any range between the two
  • the reaction time is optionally 90min, 100min, 110min, 120min, 130min, 140min, 150min Or a range between any two, when the reaction temperature is selected to be slightly higher, the reaction time is appropriately selected to be shorter; when the reaction temperature is selected to be slightly lower, the reaction time is appropriately selected to be longer, its sodium Good ion shielding and silicic acid gelation effect.
  • the reaction solution was filtered, and the filtrate was acidified and gelled.
  • the precursor is obtained after standing and aging.
  • the time for standing and aging is 1-7d, for example, optionally any one or a range between any one of 1d, 2d, 3d, 4d, 5d, 6d, and 7d.
  • the precursor is dried, and after the precursor is dried, the silicic acid shrinks to form silica, thereby forming a silica aerogel with a pompon-like porous structure, resulting in a large specific surface area and low thermal conductivity of the product.
  • any one of normal temperature natural drying, microwave drying or high temperature anaerobic drying is used for drying, but it is not limited thereto. Until the moisture content of the product after drying is less than 0.01%.
  • Natural drying at room temperature Natural drying at room temperature, the drying time is optionally 1-28d, such as any one of 1d, 4d, 7d, 10d, 14d, 17d, 20d, 23d, 25d, 28d or Any range between the two.
  • the microwave drying is microwave hot air drying.
  • the drying temperature is 160-200 ° C and the drying time is 40-80min.
  • the drying temperature is optionally 160 ° C, 165 ° C, 170 ° C, 175 ° C, 180 ° C, 185 ° C, 190 ° C, 195 ° C, 200 ° C, or a range between any two, and the drying time
  • High-temperature anaerobic drying needs to be carried out under a protective gas atmosphere with low reactivity such as nitrogen and argon.
  • the high temperature refers to a condition of a temperature of 600-800 ° C, preferably 650-750 ° C, and more preferably about 700 ° C.
  • the drying time optionally does not exceed 240 min.
  • the drying temperature is optionally any one of 600 ° C, 620 ° C, 640 ° C, 660 ° C, 680 ° C, 700 ° C, 720 ° C, 740 ° C, 760 ° C, 780 ° C, and 800 ° C Or any range between the two, the drying time is optionally 120min, 140min, 160min, 180min, 200min, 220min, 240min or any range between any two.
  • the reaction solution is filtered, acidified and gelatinized, and then the low-boiling-point organic solvent is used to replace the acidified and gelled product of the filtrate.
  • the low boiling point solvent includes at least one of ethanol, pentane, diethyl ether, acetone, and dichloromethane, but is not limited thereto.
  • ethanol and / or pentane are used.
  • Using a low-boiling organic solvent to acidify the water in the gelled product and then drying it can make the organic solvent volatilize to retain the porous structure in the precursor, thereby obtaining an aerogel with high porosity and low thermal conductivity. It is about 25 °C and the time is about 30h, which is convenient for fully replacing the water.
  • the modification treatment is optionally performed with nitrogen silane.
  • the high temperature resistance of the aerogel obtained after surface treatment is greatly improved, and the high temperature resistance can reach 1600 ° C.
  • the nitrosilane includes at least one of hexamethyldiazosilane, azidotrimethylsilane, and hexamethylcyclotrisilazane, but is not limited thereto.
  • the ratio of the amount of nitrogen silane to the amount of sodium silicate in the sodium silicate solution does not exceed 1, the reaction temperature of the surface treatment is 500-800 ° C, and the reaction time of the surface treatment is 1-60min.
  • the mass of nitrogen silane is 0.1 times, 0.2 times, 0.3 times, 0.4 times, 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times, or any two of the mass of sodium silicate.
  • the range of the reaction temperature is optionally 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C or any range between the two
  • the reaction time is optionally 1min, 5min, 10min, 20min, 30min, 40min, 50min, 60min, or any range between the two, when the reaction temperature selects a slightly higher temperature, the reaction time appropriately selects a shorter time; when the reaction When the temperature is selected to be slightly lower, the reaction time is appropriately selected for a longer time to ensure a better surface treatment effect, and the high temperature resistance of the aerogel after surface treatment reaches 900-1600 ° C.
  • the preparation method of the basic scheme E when preparing the product, is gelled at near normal temperature and dried under normal pressure, and the process is simple.
  • the cation exchange resin removes sodium ions and promotes gelation to reduce the generation of waste liquid.
  • the silica aerogel produced by the above basic scheme and improvement scheme accordingly has the advantages of simple process, environmental protection, low cost, large specific surface area and low thermal conductivity.
  • FIG. 1 Schematic diagram of the basic scheme
  • FIG. 5 Schematic diagram of the improvement process of the preferred option 4.
  • FIG. 16 is a schematic flowchart of the preferred solution 4.
  • the precursor was dried with microwave hot air at a drying temperature of 180 ° C for 60 minutes to obtain an aerogel powder with a water content of less than 0.01%.
  • the precursor was dried with microwave hot air at a drying temperature of 200 ° C for 40 minutes to obtain an aerogel powder with a water content of less than 0.01%.
  • the precursor was dried with microwave hot air at a drying temperature of 190 ° C for 50 min to obtain an aerogel powder with a water content of less than 0.01%.
  • system A 100 g of sodium silicate and 5 g of silicon phosphate were mixed uniformly, and then dissolved in 100 mL of deionized water to obtain system A. Adding 10g of nano-scale white carbon black to the A system to obtain a precursor, the precursor is atomized and dried at a temperature of 500 ° C, and the silica aerogel powder is obtained after drying.
  • system A 100 g of sodium silicate and 20 g of silicon phosphate were mixed uniformly, and then dissolved in 100 mL of deionized water to obtain system A.
  • system A 16 g of nano-scale white carbon black and 4 g of micro-silica powder were added and reacted to obtain a precursor.
  • the precursor was atomized and dried at a temperature of 300 ° C. After drying, silica aerogel powder was obtained.
  • system A 100 g of sodium silicate and 10 g of silicon phosphate were mixed uniformly, and then dissolved in 100 mL of deionized water to obtain system A. Add 15g of micro-silica powder to the system A and react to obtain a precursor. The precursor is atomized and dried at a temperature of 250 ° C. After drying, a silica aerogel powder is obtained.
  • the sodium silicate solution with a pH value of 11.3 is mixed with the silicon micropowder, stirred and kept at a temperature of 35 ° C for 2 hours, and kept stirring during the holding process. After holding, it was cooled to room temperature, and then acetic acid was slowly added to the reaction system to control the pH of the gel process to 6.8 to obtain an aerogel precursor.
  • the aerogel precursor is mixed with methane, and methane is used to replace the moisture in the precursor, and then microwave drying is performed to obtain a silica aerogel, and the evaporated methane is cooled and recovered for recycling.
  • the sodium silicate solution with a pH value of 12 was mixed with the silicon fine powder, stirred and kept at a temperature of 90 ° C for 2 hours, and kept stirring during the heat preservation. After holding, it was cooled to room temperature, and then citric acid was slowly added to the reaction system to control the pH of the gel process to 6.5 to obtain an aerogel precursor.
  • the aerogel precursor is mixed with ethanol, the water in the precursor is replaced with ethanol, and then microwave drying is performed to obtain a silica aerogel, and the evaporated ethanol is cooled and recovered for recycling.
  • the sodium silicate solution with a pH value of 13.2 was mixed with white carbon black, stirred and kept at a temperature of 65 ° C for 2 hours, and kept stirring during the holding process. After holding, it was cooled to room temperature, and then citric acid was slowly added to the reaction system to control the pH of the gel process to 6.7 to obtain an aerogel precursor.
  • the aerogel precursor is mixed with dichloromethane, the water in the precursor is replaced with dichloromethane, and then microwave drying is performed to obtain a silica aerogel, and the evaporated dichloromethane is cooled and recovered for recycling.
  • the prepared silica aerogel was observed under a scanning electron microscope to obtain an SEM image.
  • the precursor was naturally dried at room temperature for 14 days to obtain an aerogel powder with a water content of less than 0.01%.
  • the precursor was naturally dried at room temperature for 14 days to obtain an aerogel powder with a water content of less than 0.01%.
  • the precursor was naturally dried at room temperature for 14 days to obtain an aerogel powder with a water content of less than 0.01%.
  • system A 100 g of sodium silicate and 10 g of silicon phosphate were mixed uniformly, and then dissolved in 150 mL of deionized water to obtain system A. Add 5g of micro-silica powder to the system A and react to obtain a precursor. The precursor is atomized and dried at a temperature of 250 ° C. After drying, a silica aerogel powder is obtained.
  • system A 100 g of sodium silicate and 10 g of silicon phosphate were mixed uniformly, and then dissolved in 150 mL of deionized water to obtain system A.
  • 10 g of microsilica powder and 20 g of nano-scale white carbon black were added and reacted to obtain a precursor.
  • the precursor was coated on a solid surface and naturally dried. After drying for 7 days, a silica aerogel film was obtained.
  • system A 100 g of sodium silicate and 5 g of silicon phosphate were mixed uniformly, and then dissolved in 150 mL of deionized water to obtain system A.
  • system A 10 g of microsilica powder and 20 g of nano-scale white carbon black were added and reacted to obtain a precursor.
  • the precursor was coated on a solid surface and naturally dried. After drying for 7 days, a silica aerogel film was obtained.
  • silica aerogel powders prepared in Examples 4-6 and Examples 13-16 were observed under a scanning electron microscope to obtain SEM images, please refer to FIGS. 9-15.
  • Figures 9 to 15 are the electron micrographs of the samples corresponding to Examples 4-6 and Examples 13-16, respectively. It can be seen from the figure that the samples all form a porous structure, and the voids of the samples of Figures 11 and 12 are evenly distributed, without The phenomenon of agglomeration has formed a three-dimensional pore structure as a whole.
  • Example 1 800 95% 0.019
  • Example 2 850 95% 0.018
  • Example 3 820 95% 0.019
  • Example 4 950 95% 0.012
  • Example 5 860 96% 0.015
  • Example 6 870 95% 0.014
  • Example 7 500 87% 0.025
  • Example 9 856 93% 0.016
  • Example 10 900 92% 0.013
  • Example 11 800 91% 0.015
  • Example 12 700 90% 0.016
  • Example 13 920 95% 0.013
  • Example 14 900 95% 0.013
  • Example 15 870 96% 0.016
  • Example 16 900 95% 0.012

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Abstract

一种二氧化硅气凝胶制备方法，包括以下步骤：A)使用含有固态硅源、碱性溶液的原料，混合后制成气凝胶前驱体；B)将气凝胶前驱体进行干燥，制得二氧化硅气凝胶。一种改进的二氧化硅气凝胶制备方法，包括以下步骤：A)使用阳离子交换树脂和硅酸盐溶液作为原料进行混合；B)将混合后的物质静置，得到气凝胶前驱体；C)将气凝胶前驱体进行干燥，干燥后制得二氧化硅气凝胶。

Description

一种二氧化硅气凝胶制备方法及应用该方法制备的气凝胶 技术领域
本发明属于气凝胶制备领域，且特别涉及一种二氧化硅气凝胶制备方法及应用该方法制备的气凝胶。
背景技术
气凝胶通常是指将水凝胶结构体中的液体通过一定方法排除，而纳米级孔径不被破坏。获得三维网络结构的多孔介质，具有密度小、比表面积巨大，纳米级孔径等特殊特性。二氧化硅气凝胶固体，含有99％的气体，在瑞利散射作用下，显示蓝色，又被称之为蓝烟，外观看起来像云一样。气凝胶因其半透明的色彩和超轻重量，有时也被称为“固态烟”或“冻住的烟”。气凝胶可应用于航空、建筑隔热、声学延迟、环保吸附等领域。
二氧化硅气凝胶是常见的气凝胶。SiO2气凝胶是一种防热隔热性能非常优秀的轻质纳米多孔非晶固体材料，其孔隙率高，比表面积大，而密度低，室温导热系数低。正是由于这些特点使气凝胶材料在热学、声学、光学、微电子、粒子探测方面有很广阔的应用潜力。气凝胶的制备通常由溶胶凝胶过程和超临界干燥处理构成。在溶胶凝胶过程中，通过控制溶液的水解和缩聚反应条件，在溶体内形成不同结构的纳米团簇，团簇之间的相互粘连形成凝胶体，而在凝胶体的固态骨架周围则充满化学反应后剩余的液态试剂。气凝胶的生成机理是在干燥过程中既要使前期形成的凝胶脱水，又要保证凝胶不塌陷，从而使空气进入凝胶网络中替代原凝胶内水的位置。
目前，现有技术中应用超临界干燥工艺的气凝胶制备方法通常以正硅酸甲酯、正硅酸乙酯为硅源制备二氧化硅气凝胶。这些有机硅源需要水解才能产生硅酸，在水解过程中会产生大量的挥发性有机物，在混合以及干燥过程 中会大量排放挥发性有机废气。现有技术中，还有采用硅酸钠溶液作为硅源的工艺流程，硅酸钠作为原料会大量使用，从而导致过中间产品的钠离子过量，过量的钠离子若进入最终的产品会使产品对金属造成腐蚀性，为保证产品质量需要对钠离子进行清除，钠离子的清洗过程通常会产生大量的废水。现有技术中还有主要选择二甲基氯硅烷作为前驱体原料的，这种原料本身水解会产生大量的氯离子，氯离子同样具有较强的腐蚀性，过量的氯离子若留存在产品内会影响产品质量。为清除氯离子，需要使用大量的液体进行清洗，因而产生大量含氯废液。
发明内容
相关术语
硅源:可以为二氧化硅气凝胶的产生过程提供硅元素的物质。
固态硅源：固态硅源可以是白炭黑、硅微粉、硅藻土固态含硅化合物，或者以上材料的混合物，有很大的反应接触面，可以在碱离子作用下形成硅酸离子。
碱性溶液：本文中所指的碱性溶液包括碱性水溶液(如氢氧化钠溶液、硅酸钠溶液)，碱性有机溶液(如溶于乙醇的乙醇钠溶液)，以及以上两种溶液的混合物。
基础技术方案A
在现有技术中，以有机硅源(如正硅酸甲酯、正硅酸乙酯)为原料的二氧化硅气凝胶制备方法，会使用大量的有机物，在物料混合、搅拌、干燥等工序中会产生大量有机废气。在采用硅酸钠溶液作为硅源的现有技术中，硅酸钠作为原料会大量使用，从而导致过中间产品的钠离子过量，过量的钠离子若进入最终的产品会使产品对金属造成腐蚀性，为保证产品质量需要对钠离子进行清除，钠离子的清洗过程通常会产生大量的废水。废水量大的问题 也出现在使用其他硅酸盐作为硅源的二氧化硅气凝胶制备工艺中。
为解决以上有机废气或废水大量产生的问题，本技术方案使用了一种使用固态硅源作为提供硅元素的原材料，使之与碱性溶液在一定条件下进行混合，混合后得到气凝胶前驱体，前驱体凝胶反应后，再经过干燥后制得气凝胶产品，其步骤如下:
A.固态硅源与碱性溶液在一定条件下进行混合，混合后得到气凝胶前驱体。
B.前驱体进行干燥得到气凝胶产品。
固态硅源可以在碱离子作用下形成硅酸根离子，硅酸根离子极不稳定，遇到氢离子迅速结合为硅酸，控制一定条件，硅酸经过凝胶反应形成凝胶体。本技术方案由于使用固态硅源可以提供非常大的反应接触面，提高捕捉碱离子的机会，加速硅酸离子的形成；同时多孔介质为多分子凝集体，具有较大的吸附能力，形成的硅酸离子容易被多孔介质捕捉，被吸附在多孔介质表面。凝胶反应主要为界面反应如在固-液界面发生凝胶反应。凝胶后采用干燥(可采用多种干燥方式)获得二氧化硅气凝胶的方法。即多孔二氧化硅固体介质一部分作为反应物参与反应，一部分作为种子吸附新生成的二氧化硅。从而有大孔径多孔介质形成小孔径的水凝胶体。
相比于现有技术中使用有机硅源(如正硅酸甲酯、正硅酸乙酯)为原料的二氧化硅气凝胶制备方法，本技术方案减少了原材料中有机物的添加，从而在混合、搅拌、以及干燥工艺过程中避免了大量有机废气的产生。
相比于现有技术中使用无机硅酸纳作为主要硅源原料的二氧化硅气凝胶制备方法，本技术方案由于使用固态硅源作为硅源，因而避免了在产品中出现钠离子过量的风险，从而不需要进行钠离子的清洗，避免了大量含钠废水的产生。
此外，由于本技术方案的凝胶反应主要发生在固-液界面，所以可以通 过控制固液比例来控制反应速度，因而可以在优化控制的前提下使产品的比表面积增大、导热系数降低，整体提升产品质量。
方案B：磷酸硅类调节剂改进
方案B是基础技术方案A的改进，在使用固态硅源作为主要原料的情况下，其他原料还有磷酸硅、硅酸钠和水。方案B的步骤如下:
A.在密封状态下，将混合均匀的磷酸硅、硅酸钠和水，与凝胶核粒子固态硅源混合得到前驱体。
B.前驱体进行干燥得到气凝胶产品。
方案B中的磷酸硅可以用聚磷酸硅，或磷酸硅与聚磷酸硅的混合物替换。
方案B可以减少废液的主要原因有，固态硅源硅酸钠和磷酸硅的水溶液中反应，会生成需要的产物硅酸。磷酸硅与水反应水解生成磷酸和硅酸，磷酸在水中可以生成氢离子，此时的溶液中还存在大量的硅酸根粒子，氢离子与溶液中的硅酸根离子也可以生成产物硅酸。在这个过程中没有引入更多的溶液，同时原料中的含硅元素都可以转化为最终物硅酸，相比于现有技术中应用硅酸钠作为硅源的二氧化硅气凝胶制备方法，方案B减少了去除溶液中硅酸盐的步骤，从而减少了废液的产生。
固态硅源的白炭黑和硅微粉中的一种或两种，白炭黑和硅微粉中均主要含有二氧化硅，且均为多孔结构，白炭黑以及硅微粉与钠离子反应生成硅酸钠，硅酸钠继续水解得到硅酸。对前驱体干燥后，硅酸缩水形成二氧化硅，同时，白炭黑和硅微粉作为凝胶核粒子吸附缩水后得到的二氧化硅，从而形成多孔结构的二氧化硅气凝胶，该过程避免了废液的产生。
在方案B中，磷酸硅与硅酸钠的质量比为1～100:100；凝胶核粒子与硅酸钠的重量比为1～50:100。磷酸硅与硅酸钠的质量比为5～50:100。磷酸硅与硅酸钠的质量比为10～30:100。该比例范围的磷酸硅与硅酸钠制得的二氧化硅凝胶比表面积更大，导热系数更小。
在方案B中，凝胶核粒子与硅酸钠的重量比为5～20:100，该比例范围的凝胶核粒子与硅酸钠制得的二氧化硅凝胶比表面积更大，导热系数更小。
进一步地，在方案B中，二氧化硅气凝胶可通过雾化干燥或者自然干燥得到。其中，雾化干燥得到的是粉状二氧化硅气凝胶，干燥温度可选择200～500℃，此温度范围内进行干燥能够得到质量较好的二氧化硅气凝胶。
当然，也可以在使用时，直接将前驱体涂敷于固体表面进行自然干燥，在室温下初始凝胶40～50h，最终干燥时间为6～7天。
其由上述的二氧化硅气凝胶的制备方法制得，制得的二氧化硅气凝胶为多孔结构。该结构特征使得二氧化硅气凝胶具有较大的比表面积和较小的导热系数。
方案C：酸性调节剂改进
方案C是基础技术方案A的一种改进方案，在使用固态硅源作为主要原料的情况下，其他原料还有酸性调节剂、低沸点有机溶剂。方案C的步骤如下:
A.将呈碱性的硅酸盐水溶液与固体硅源在35～100℃的条件下反应，硅酸盐包含但不局限于硅酸钠、硅酸钾、硅酸锂等相关金属硅酸盐。
B.在A步骤反应得到的物质冷却至室温后，加入酸性物质调节pH值至6.5～7.5反应，反应得到前驱体。酸性物质包括盐酸、硫酸、磷酸、硝酸中、醋酸、柠檬酸和苯甲酸中的任一种。
C.前驱体凝胶后，利用低沸点有机溶剂对前驱体进行溶剂置换，将前驱体中的水分置换出来，低沸点有机溶剂包括乙醇、戊烷、二氯甲烷或甲醇中的任一种。
D.将经过有机溶剂置换的前驱体进行干燥得到气凝胶产品。
方案C可以减少废液的主要原因是，首先固态硅源在碱性的硅酸盐溶液中反应，会生成所需产物硅酸，此时的硅酸盐是催化剂的作用。这时的碱性 溶液中还存在大量的硅酸根粒子，再向其中加入酸性物质，酸性物质提供的氢离子与硅酸根离子结合又会生成所需硅酸。相比于现有技术中应用硅酸钠作为硅源的二氧化硅气凝胶制备方法，方案C减少了硅酸钠溶液的使用，从而减少了在后续清洗钠离子环节液体的使用，从而减少了废液的产生。
将呈碱性的硅酸类物质溶液与固态硅源在35～100℃的条件下反应，冷却至室温后加入酸性物质调节pH值为6.5～7.5，反应得到前驱体；其中，硅酸类物质包括硅酸或硅酸盐。示例性地，硅酸盐可以为硅酸钠、硅酸钾、硅酸钙等。其中，硅酸盐溶液为硅酸盐的水溶液，硅酸盐在水中水解使得溶液呈碱性。其中，硅酸溶液由硅酸溶于酸溶液得到。
硅酸类物质溶液为碱性溶液，在方案C中，硅酸类物质溶液的pH值为10～14。二氧化硅源在35～100℃温度及碱性条件下溶解反应形成硅酸。冷却至室温后加入酸性物质，酸性物质提供氢离子，氢离子取代硅酸类物质的盐离子从而生成硅酸，继而得到前驱体。前驱体凝胶后，利用低沸点有机溶剂对前驱体进行溶剂置换将前驱体中的水分置换出来，然后进行干燥可使得有机溶剂挥发从而保留前驱体中的多孔结构，从而得到空隙率高、比表面积大的二氧化硅气凝胶。
在方案C中，干燥方式为微波干燥，微波进入凝胶并被吸收后，其能量在物料电介质内部转换成热能，微波干燥的热传导方向与有机溶剂扩散方向相同，热量能均匀渗透，具有干燥速率大，干燥均匀的效果。
在方案C中，二氧化硅源包括白炭黑和硅微粉中的一种或多种。其中，白炭黑和硅微粉中的主要成分均为二氧化硅，且均为多孔结构。白炭黑和硅微粉的粒度为纳米级，在35～100℃温度及碱性条件下溶解反应形成硅酸。在一些实施方式中，硅酸类物质溶液与二氧化硅源的反应温度为50～90℃。硅酸类物质溶液与二氧化硅在该温度范围内反应，二氧化硅源能够较好地溶解彻底反应生成硅酸。
进一步地，在方案C中，酸性物质包括有机酸和/或无机酸。也即是说，酸性物质可以为有机酸，也可以为无机酸，也可以为有机酸和无机酸的混合物。其中，无机酸包括盐酸、硫酸、磷酸和硝酸中的任一种。有机酸包括醋酸、柠檬酸和苯甲酸中的任一种。
另外，在方案C中，低沸点有机溶剂包括乙醇、戊烷、二氯甲烷或甲醇中的任一种。
低沸点有机溶剂的沸点较低，在进行干燥时，在温度较低的情况下也能将低沸点有机溶剂去除，从而达到更好的干燥效果。
其由上述的利用酸性物质改性硅酸类物质制备二氧化硅气凝胶的方法制得的一种二氧化硅气凝胶，该方法制备得到的气凝胶具有多孔结构，经测试，具有较大的比表面积和较小的导热系数。
方案D：有机酯改性
方案D是基础技术方案A的改进，在使用固态硅源作为主要原料的情况下，原料中还可以加入硅酸钠，以及有机酯用于改性，生产改性硅酸钠气凝胶。方案D的步骤如下:
A.将硅酸钠、固态硅源的混合物与有机酯进行水解反应得到前驱体。
B.前驱体进行干燥得到气凝胶产品。
方案D中的硅酸钠还可以用硅溶胶替换。
方案D可以减少废液的主要原因是，首先固态硅源在碱性的硅酸盐溶液中反应，会生成所需产物硅酸，硅酸钠与水反应水解生成硅酸并提供氢氧根离子，主要起到对反应的催化效果。有机酯水解反应中生成的酸在水中可以生成氢离子，此时的溶液中还存在大量的硅酸根粒子，氢离子与溶液中的硅酸根离子也可以生成所需的产物硅酸。在这个过程中没有引入更多的溶液，同时原料中的含硅元素都可以转化为最终物硅酸，从而减少了去除溶液中硅酸盐的步骤，从而减少了废液的产生。相比于现有技术中应用硅酸钠作为硅 源的二氧化硅气凝胶制备方法，方案D减少了硅酸钠溶液的使用，从而减少了在后续清洗钠离子环节液体的使用，从而减少了废液的产生。相比于现有技术中应用有机硅源作为硅源的二氧化硅气凝胶制备方法，方案D中的有机酯作为催化剂，有机物使用量相对较少，从而减少了在相关工艺环节中有机废气的产生量。
同时有机酯水解产生的酸可有效控制凝胶速度，可通过酸碱性的调节控制水解速度，制得的产品品质可控，可根据需要生产不同品质的气凝胶。
利用有机酯水解的特点，可以为反应提供氢离子，改变直接用酸凝胶的方法；有机酯水解提供醇的特点。有机酯水解产生的醇能替代溶剂置换乙醇等低沸点有机溶剂，原料简单、工艺简便。使得工艺简化变为一步法，取代传统用有机溶剂置换凝胶内的液体二步法工艺，从而减少工艺过程，降低生产周期，提高了生产效率，降低了生产成本。方法制备产品时在常温下凝胶且在常压下干燥，工艺简单。方法为：将硅酸盐和固态硅源的混合物与水解的有机酯进行应得到前驱体，将前驱体进行干燥进而制得二氧化硅气凝胶。优选方案一种所述硅酸盐可以为硅酸钠、硅酸钾、硅酸钙等，优选的硅酸盐为硅酸钠。
采用有机酯进行改性，有机酯水解的速度可通过浓度、温度、酸碱性等进行调节。有机酯水解反应中，添加如三乙酸铵等酸碱指示剂进行酸碱性的调节。同时可以添加模板导向剂如烷基苯磺酸(或金属盐)，和/或，模板剂如聚乙烯醇，该模板导向剂、导向剂在有机酯水解反应的体系中的总的质量分数为0～20％。有机酯水解反应中生成的酸可有效控制凝胶速度，从而控制产品的比表面积、孔径以及结构形态，通过调节控制有机酯的水解速度，制得的产品品质可控，可根据需要生产不同品质的气凝胶。有机酯水解产生的醇能替代溶剂置换中乙醇等低沸点有机溶剂，原料简单、工艺简便。
有机酯可以是任意的能够水解的有机酯类。有机酯例如但不限于包含以 下种类的酯类中的至少一种：例如根据酯基的种类不同划分的有机硅酯和有机酸酯中的至少一种。上述的有机硅酯和有机酸酯例如可以是但不限于R基团仅含碳链结构的常规酯类和R基团含有芳基的芳香族酯等中的至少一种。本发明中的有机酸酯是指常规的由羧基和“-C-OH”醇羟基缩合生成酯基的酯类，如根据羧酸部分的“元”数划分为一元酸酯、二元酸酯和其他的多元酸酯。
较佳地，有机酯为低分子量的液态酯，上述的低分子量是指只要能够使有机酯在常温常压下呈现液态即可，其方便水解反应的操作。高分子量的酯一般为固态，制备繁琐，工艺复杂。
进一步地，有机酯较佳地选择有机硅酯、一元酸酯、二元酸酯中的至少一种。例如但不限于以下情况，可选地包括乙酸乙酯、乙酸甲酯、甲酸乙酯、丙二酸甲酯、丙二酸乙酯、丁二酸甲酯、丁二酸乙酯、乙酸三甲基硅甲基酯、甲硅烷基溴代乙酸三甲酯、甲基丙烯酸三甲基硅酯、异丁酸三甲基硅酯、丙酸三甲基硅酯、异硫氢酸三甲基硅酯等中的至少一种。
模板导向剂如烷基苯磺酸(或金属盐)起到润湿，增加表面接触的机会。白炭黑微粒成为局部反应的载体和凝胶载体。聚乙烯醇的多羟基起到模板作用，引导硅酸形成环状立体结构体。
方案D中，白炭黑为亲水和/或疏水白炭黑，如可以仅采用疏水白炭黑，或者可以采用疏水白炭黑和亲水白炭黑混和，或者采用仅采用亲水白炭黑，当添加有亲水白炭黑特别亲水白炭黑较多的情况下可以添加有机硅疏水剂来达到疏水的目的，使该白炭黑可溶于有机酯中，从而达到使粒子重新排布，生成多孔介质，胶凝效果更佳。
方案D中，硅酸钠的用量较少，硅酸钠与水反应水解生成硅酸并提供氢氧根离子，主要起到对反应的催化效果。
可选地，硅酸钠和白炭黑的质量比为18-38：40-60。白炭黑与有机酯的 质量比为40-60：90-110。白炭黑与水解反应中的水的质量比为40-60：90-110。
进一步地，在方案D的实施方式中，硅酸钠、白炭黑、有机酯以及水解反应中的水的质量比依次为18-38：40-60：90-110：90-110。优选地依次为23-33：45-55：95-105：95-105。更优选地依次为28：50：100：100。
在方案D的具体的实施方式中，水解反应于密闭条件下持续搅拌进行，反应温度为50-70℃，反应时间为3-5h。水解反应在密闭容器中进行，防止有机物挥发。反应温度可选地为50℃、52℃、54℃、56℃、58℃、60℃、62℃、64℃、66℃、68℃、70℃中的任意一者或任意两者之间的范围，反应时间可选地为3h、3.5h、4h、4.5h、5h中的任意一者或任意两者之间的范围，水解效果较佳。
可选地，干燥采用微波热风干燥，干燥温度为160-200℃，干燥时间为40-80min，干燥后产物含水量低于0.01％。干燥温度可选地为160℃、165℃、170℃、175℃、180℃、185℃、190℃、195℃、200℃中的任意一者或任意两者之间的范围，干燥时间可选地为40min、45min、50min、55min、60min、65min、70min、75min、80min中的任意一者或任意两者之间的范围，保证充分干燥，使干燥后的产品具有较好的多孔结构。
基础方案E：阳离子交换树脂改进
本发明的另一种改进方案为，硅源除了是固态硅源外，硅源包含但不局限于硅酸钠、硅酸钾、硅酸锂等相关无机硅酸盐原料还包括水与阳离子交换树脂。流程包括：
A.将硅酸盐溶液与阳离子交换树脂粉体进行离子交换反应。
B.反应后静止陈化得到前驱体。
C.将前驱体进行干燥，得到二氧化硅气凝胶。
基础方案E一种所述硅酸盐可以为硅酸钠、硅酸钾、硅酸钙等，优选的硅酸盐为硅酸钠。
采用阳离子交换树脂与硅酸钠溶液进行离子交换反应，离子交换树脂吸附硅酸钠溶液中的钠离子并向溶液中释放氢离子，释放的氢离子取代硅酸钠的钠离子从而生成硅酸酸化胶凝。阳离子交换树脂清除钠离子并促进凝胶化，减少废液的产生，绿色环保。采用离子树脂屏蔽钠离子或金属离子，可以减少后续去除阳离子的步骤，减少废液产生，最终提高产品质量，降低了产品对金属材料的腐蚀可能性。相比于现有技术中应用硅酸钠作为硅源的二氧化硅气凝胶制备方法，基础方案E减少了硅酸钠溶液的使用，从而减少了在后续清洗钠离子环节液体的使用，从而减少了废液的产生。
基础方案E中，硅酸钠溶液的浓度为0到饱和状态，可选地不超过4.5mol/L，例如为0.1mol/L、0.5mol/L、1mol/L、1.5mol/L、2mol/L、2.5mol/L、3mol/L、3.5mol/L、4mol/L、4.5mol/L中的任意一者或两者之间的范围。硅酸钠溶液中硅酸钠与阳离子交换树脂粉体的质量比值不超过100，例如硅酸钠的质量为阳离子交换树脂的1倍、10倍、20倍、30倍、40倍、50倍、60倍、70倍、80倍、90倍、100倍中的任意一者或两者之间的范围。
进一步地，离子交换反应于搅拌条件下进行，反应温度为25-90℃，反应时间为1.5-2.5h。例如，在本发明一些具体的实施方式中，反应温度可选地为25℃、30℃、35℃、40℃、45℃、50℃、55℃、60℃、65℃、70℃、75℃、80℃、85℃、90℃、95℃中的任意一者或任意两者之间的范围，反应的时间可选地为90min、100min、110min、120min、130min、140min、150min中的任意一者或任意两者之间的范围，当反应温度选择稍高的温度时反应时间适当地选择较短的时间；当反应温度选择稍低的温度时反应时间适当地选择较长的时间，其钠离子屏蔽及硅酸胶凝效果好。
离子交换反应之后将反应液进行过滤，滤液酸化胶凝。静置陈化后得到前驱体。可选地，静置陈化的时间为1-7d，例如可选地为1d、2d、3d、4d、5d、6d、7d中的任意一者或任意两者之间的范围。将前驱体进行干燥，前驱 体干燥后硅酸缩水形成二氧化硅，从而形成绒球状多孔结构的二氧化硅气凝胶，使产品的比表面积大、导热系数低。
基础方案E中，干燥采用常温自然干燥、微波干燥或高温无氧干燥中的任一种，但不限于此。直至干燥后产品的含水量低于0.01％。
常温自然干燥在室温下自然干燥，干燥的时间可选地为1-28d，例如可选地为1d、4d、7d、10d、14d、17d、20d、23d、25d、28d中的任意一者或任意两者之间的范围。
微波干燥为微波热风干燥，可选地，干燥温度为160-200℃，干燥时间为40-80min。例如，干燥温度可选地为160℃、165℃、170℃、175℃、180℃、185℃、190℃、195℃、200℃中的任意一者或任意两者之间的范围，干燥时间可选地为40min、45min、50min、55min、60min、65min、70min、75min、80min中的任意一者或任意两者之间的范围。
高温无氧干燥需要在氮气、氩气等反应活性低的保护气体氛围下进行。其高温是指温度为600-800℃的条件，优选地为650-750℃，更优选地为约700℃。干燥的时间可选地不超过240min。在一些具体的实施方式中，干燥温度可选地为600℃、620℃、640℃、660℃、680℃、700℃、720℃、740℃、760℃、780℃、800℃中任意一者或任意两者之间的范围，干燥时间可选地为120min、140min、160min、180min、200min、220min、240min中任意一者或任意两者之间的范围。
基础方案E中，离子交换反应后且静止陈化之前，将反应液进行过滤酸化胶凝后，采用低沸点有机溶剂对滤液酸化胶凝后的产物进行溶剂置换。
可选地，低沸点溶剂包括乙醇、戊烷、乙醚、丙酮和二氯甲烷中的至少一种，但不限于此。优选地，采用乙醇和/或戊烷。利用低沸点有机溶剂酸化胶凝产物中的水分置换出来，然后进行干燥可使得有机溶剂挥发从而保留前驱体中的多孔结构，从而得到空隙率高、导热系数小的气凝胶。约25℃，时 间约为30h，便于将水分充分置换出来。
在溶剂置换之后且静止陈化之前，可选地，采用氮硅烷进行改性处理。表面处理后得到的气凝胶的耐高温性能大大提高，耐高温可达1600℃。
在一些具体的实施方式中，氮硅烷包括六甲基二氮硅烷、叠氮基三甲基硅烷和六甲基环三硅氮烷中的至少一种，但不限于此。氮硅烷的用量与硅酸钠溶液中的硅酸钠的用量之比值不超过1，表面处理的反应温度为500-800℃，表面处理的反应时间为1-60min。例如氮硅烷的质量为硅酸钠质量的0.1倍、0.2倍、0.3倍、0.4倍、0.5倍、0.6倍、0.7倍、0.8倍、0.9倍、1倍中的任意一者或任意两者之间的范围，反应温度可选地为500℃、550℃、600℃、650℃、700℃、750℃、800℃中的任意一者或任意两者之间的范围，反应时间可选地为1min、5min、10min、20min、30min、40min、50min、60min中的任意一者或任意两者之间的范围，当反应温度选择稍高的温度时反应时间适当地选择较短的时间；当反应温度选择稍低的温度时反应时间适当地选择较长的时间，以保证较好的表面处理效果，使表面处理后的气凝胶的耐高温达到900-1600℃。
基础方案E的制备方法，制备产品时，在接近常温下凝胶且在常压下干燥，工艺简单。阳离子交换树脂清除钠离子并促进凝胶化，减少废液的产生。
由上述基础方案以及改进方案制得的二氧化硅气凝胶，相应地具备工艺简单、绿色环保、成本低，且比表面积大、导热系数低等优点。
附图说明
图1基础方案流程示意图
图2优选方案1流程示意图
图3优选方案2流程示意图
图4优选方案3流程示意图
图5优选方案4的改进流程示意图
图6实施例7的二氧化硅气凝胶的SEM图
图7实施例8的二氧化硅气凝胶的SEM图
图8实施例9的二氧化硅气凝胶的SEM图
图9实施例4的二氧化硅气凝胶的SEM图
图10实施例5的二氧化硅气凝胶的SEM图
图11实施例6的二氧化硅气凝胶的SEM图
图12实施例13的二氧化硅气凝胶的SEM图
图13实施例14的二氧化硅气凝胶的SEM图
图14实施例15的二氧化硅气凝胶的SEM图
图15实施例16的二氧化硅气凝胶的SEM图
图16优选方案4流程示意图。
具体实施方式
实施例1
将28g硅酸钠和50g甲基丙烯酸甲酯改性白炭黑混合均匀，向混合物中加入100g乙酸乙酯和100g水，在密闭容器中、反应温度为60℃的搅拌状态下反应4h，得到前驱体。
将前驱体利用微波热风干燥在干燥温度为180℃的条件下干燥60min，得到含水量低于0.01％的气凝胶粉末。
实施例2
将18g硅酸钠和40g甲基丙烯酸甲酯改性白炭黑混合均匀，向混合物中加入90g乙酸乙酯和90g水，在密闭容器中、反应温度为50℃的搅拌状态下反应5h，得到前驱体。
将前驱体利用微波热风干燥在干燥温度为200℃的条件下干燥40min， 得到含水量低于0.01％的气凝胶粉末。
实施例3
将23g硅酸钠和45g甲基丙烯酸甲酯改性白炭黑混合均匀，向混合物中加入95g乙酸乙酯和95g水，在密闭容器中、反应温度为55℃的搅拌状态下反应4.5h，得到前驱体。
将前驱体利用微波热风干燥在干燥温度为190℃的条件下干燥50min，得到含水量低于0.01％的气凝胶粉末。
实施例4
在密封状态下，将100g硅酸钠和5g磷酸硅混合均匀，然后溶解于100mL的去离子水中得到A体系。向A体系中加入10g的纳米级白炭黑反应得到前驱体，将前驱体在500℃的温度条件下进行雾化干燥，干燥后得到二氧化硅气凝胶粉末。
实施例5
在密封状态下，将100g硅酸钠和20g磷酸硅混合均匀，然后溶解于100mL的去离子水中得到A体系。向A体系中加入16g的纳米级白炭黑及4g的微硅粉进行反应得到前驱体，将前驱体在300℃的温度条件下进行雾化干燥，干燥后得到二氧化硅气凝胶粉末。
实施例6
在密封状态下，将100g硅酸钠和10g磷酸硅混合均匀，然后溶解于100mL的去离子水中得到A体系。向A体系中加入15g的微硅粉进行反应得到前驱体，将前驱体在250℃的温度条件下进行雾化干燥，干燥后得到二氧化硅气凝胶粉末。
实施例7
将pH值为11.3的硅酸钠溶液与硅微粉混合，在35℃的温度条件下搅拌并保温2小时，在保温的过程中保持搅拌。保温后冷却至室温，然后向反 应体系中缓慢加入醋酸，，控制凝胶过程pH为6.8，得到气凝胶前驱体。将气凝胶前驱体与甲烷混合，利用,甲烷将前驱体中的水分置换出来，然后进行微波干燥得到二氧化硅气凝胶，蒸发出来的甲烷冷却回收后循环使用。
实施例8
将pH值为12的硅酸钠溶液与硅微粉混合，在90℃的温度条件下搅拌并保温2小时，在保温的过程中保持搅拌。保温后冷却至室温，然后向反应体系中缓慢加入柠檬酸，控制凝胶过程pH为6.5，得到气凝胶前驱体。将气凝胶前驱体与乙醇混合，利用乙醇将前驱体中的水分置换出来，然后进行微波干燥得到二氧化硅气凝胶，蒸发出来的乙醇冷却回收后循环使用。
实施例9
将pH值为13.2的硅酸钠溶液与白炭黑混合，在65℃的温度条件下搅拌并保温2小时，在保温的过程中保持搅拌。保温后冷却至室温，然后向反应体系中缓慢加入柠檬酸，控制凝胶过程pH为6.7，得到气凝胶前驱体。将气凝胶前驱体与二氯甲烷混合，利用二氯甲烷将前驱体中的水分置换出来，然后进行微波干燥得到二氧化硅气凝胶，蒸发出来的二氯甲烷冷却回收后循环使用。对制备得到的二氧化硅气凝胶在扫描电子显微镜下进行观察，得到SEM图。从SEM图中可以看出，固态二氧化硅源与硅酸钠重新结合后，分布均匀，形成三维结构，网状结构明显。没有硅微粉的大粒径实心粒子，说明固态二氧化硅源与硅酸钠反应完全，形成了三维孔状结构体。
实施例10
将2mol的硅酸钠投入1L水中配成硅酸钠溶液，向硅酸钠溶液中投入硅酸钠质量的1/50的阳离子交换树脂。在反应温度为50℃的搅拌状态下反应2h。离子交换反应后进行过滤，滤液酸化凝胶，加入乙醇在温度为25℃的条件下进行30h的溶剂置换，加入硅酸钠质量的1/2的六甲基二氮硅烷在温度为650℃的条件下进行30min的改性处理，然后进行4d的静置陈化，得到 前驱体。
将前驱体常温自然干燥14d，得到含水量低于0.01％的气凝胶粉末。
一种上述方法制得的气凝胶。
实施例11
将3mol的硅酸钠投入1L水中配成硅酸钠溶液，向硅酸钠溶液中投入硅酸钠质量的1/70的阳离子交换树脂。在反应温度为50℃的搅拌状态下反应2h。离子交换反应后进行过滤，滤液酸化凝胶，加入乙醇在温度为25℃的条件下进行30h的溶剂置换，加入硅酸钠质量的1/3的六甲基二氮硅烷在温度为650℃的条件下进行30min的改性处理，然后进行4d的静置陈化，得到前驱体。
将前驱体常温自然干燥14d，得到含水量低于0.01％的气凝胶粉末。
实施例12
将1mol的硅酸钠投入1L水中配成硅酸钠溶液，向硅酸钠溶液中投入硅酸钠质量的1/30的阳离子交换树脂。在反应温度为50℃的搅拌状态下反应2h。离子交换反应后进行过滤，滤液酸化凝胶，加入乙醇在温度为25℃的条件下进行30h的溶剂置换，加入硅酸钠质量的1/4的六甲基二氮硅烷在温度为650℃的条件下进行30min的改性处理，然后进行4d的静置陈化，得到前驱体。
将前驱体常温自然干燥14d，得到含水量低于0.01％的气凝胶粉末。
实施例13
在密封状态下，将100g硅酸钠和10g磷酸硅混合均匀，然后溶解于150mL的去离子水中得到A体系。向A体系中加入5g的微硅粉进行反应得到前驱体，将前驱体在250℃的温度条件下进行雾化干燥，干燥后得到二氧化硅气凝胶粉末。
实施例14
在密封状态下，将100g硅酸钠和15g磷酸硅混合均匀，然后溶解于100mL的去离子水中得到A体系。向A体系中加入1g的微硅粉进行反应得到前驱体，将前驱体在400℃的温度条件下进行雾化干燥，干燥后得到二氧化硅气凝胶粉末。
实施例15
在密封状态下，将100g硅酸钠和10g磷酸硅混合均匀，然后溶解于150mL的去离子水中得到A体系。向A体系中加入10g的微硅粉及20g的纳米级白炭黑进行反应得到前驱体，将前驱体涂敷在固体表面进行自然干燥，干燥7天后得到二氧化硅气凝胶膜。
实施例16
在密封状态下，将100g硅酸钠和5g磷酸硅混合均匀，然后溶解于150mL的去离子水中得到A体系。向A体系中加入10g的微硅粉及20g的纳米级白炭黑进行反应得到前驱体，将前驱体涂敷在固体表面进行自然干燥，干燥7天后得到二氧化硅气凝胶膜。
对实施例4-6以及实施例13-16制备得到的二氧化硅气凝胶粉末在扫描电子显微镜下进行观察，得到SEM图，请参照图9-图15。
图9至图15分别为实施例4-6以及实施例13-16对应的样品电镜图片，从图中可以看出，样品都形成了多孔结构，其中图11、12的样品空隙分布均匀，没有结团现象，整体都形成了三维孔状结构。
对实施例1-16制得的气凝胶的比表面积、孔隙率、导热系数进行测试，其结果如下表所示。
性能测试表
项目 比表面积/(m 2/g) 孔隙率 导热系数/(w/mk)
实施例1 800 95％ 0.019
实施例2 850 95％ 0.018
实施例3 820 95％ 0.019
实施例4 950 95％ 0.012
实施例5 860 96％ 0.015
实施例6 870 95％ 0.014
实施例7 500 87％ 0.025
实施例8 839 92％ 0.018
实施例9 856 93％ 0.016
实施例10 900 92％ 0.013
实施例11 800 91％ 0.015
实施例12 700 90％ 0.016
实施例13 920 95％ 0.013
实施例14 900 95％ 0.013
实施例15 870 96％ 0.016
实施例16 900 95％ 0.012

Claims (40)

  1. 一种二氧化硅气凝胶制备方法，其特征在于，包括以下步骤：
    A)使用含有固态硅源、碱性溶液的原料，混合后制成气凝胶前驱体；
    B)将气凝胶前驱体进行干燥，制得二氧化硅气凝胶。
  2. 如权利要求1所述的方法，所述步骤A)中的原料还包括磷酸硅或聚磷酸硅。
  3. 如权利要求1或2所述的方法，所述步骤A)原料中的固态硅源包括白炭黑、硅微粉、硅藻土中的一种或几种，原料的混合过程为密封状态。
  4. 如权利要求2所述的方法，所述步骤A)原材料中还包含硅酸钠，磷酸硅与硅酸钠的质量比为(1～100):100。
  5. 如权利要求1或2所述的方法，所述步骤A)原材料中还包含硅酸钠，固态硅源与硅酸钠的重量比为(1～50):100。
  6. 如权利要求1或2所述的方法，所述步骤B)干燥温度为200～500℃。
  7. 如权利要求1或2所述的方法，所述步骤B)干燥过程为雾化干燥、自然干燥的一种。
  8. 如权利要求1所述的方法，所述步骤A)原料还包括酸性物质。
  9. 如权利要求8所述的方法，所述步骤A)混合过程的反应温度区间为35～100℃。
  10. 如权利要求8或9所述的方法，所述步骤A)在混合过程后，需要冷却至室温，并加入酸性物质调节pH值为6.5～7.5，反应得到前驱体。
  11. 如权利要求1所述的方法，所述步骤B)中利用低沸点有机溶剂对所述前驱体进行溶剂置换出将所述前驱体中的水分。
  12. 如权利要求1所述的方法，所述步骤A)原材料包括硅酸盐。
  13. 如权利要求1或8所述的方法，所述步骤A)中原材料固态硅源包括白炭黑、硅微粉、硅藻土中的一种或多种；所述混合过程后溶液的pH值为10～14。
  14. 如权利要求1或8所述的方法，所述步骤A)酸性物质包括盐酸、硫酸、磷酸、硝酸中、醋酸、柠檬酸和苯甲酸中的任一种。
  15. 如权利要求1或11所述的方法，所述步骤A)低沸点有机溶剂包括乙醇、戊烷、二氯甲烷或甲醇中的任一种。
  16. 如权利要求12所述的方法，所述步骤A)硅酸盐溶液与所述固态硅源的反应温度为50～90℃。
  17. 如权利要求12所述的方法，所述步骤A)原料还包括有机酯，所述固态硅源与所述有机酯的质量比为(40-60)：(90-110)。
  18. 如权利要求17所述的方法，所述步骤A)原料中所述硅酸盐和固态 硅源的质量比为(18-38)：(40-60)。
  19. 如权利要求17所述的方法，其特征在于，所述步骤A)中固态硅源的可以是亲水白炭黑和/或疏水白炭黑，固态硅源与水解反应中的水的质量比为(40-60)：(90-110)。
  20. 如权利要求17所述的方法，所述步骤A)中有机酯包括有机硅酯、一元酸酯、二元酸酯中的至少一种。
  21. 如权利要求-17所述的方法，其特征在于，所述步骤A)中有机酯水解反应于密闭条件下持续搅拌进行，反应温度为50-70℃，反应时间为3-5h。
  22. 如权利要求1或17所述的方法，所述步骤B)的干燥采用微波热风干燥，干燥温度为160-200℃，干燥时间为40-80min，干燥后产物含水量低于0.01％。
  23. 如权利要求12所述的方法，所述步骤A)原料还包括阳离子交换树脂，原料混合后需静置。
  24. 如权利要求23所述的方法，所述步骤A)原料中硅酸盐的溶液浓度不超过4.5mol/L。
  25. 如权利要求23所述的方法，所述步骤A)原料中硅酸盐溶液中硅酸盐与所述阳离子交换树脂粉体的质量比值不超过100。
  26. 如权利要求23所述的方法，所述步骤A)中离子交换反应于搅拌条 件下进行，反应温度为25-90℃，反应时间为1.5-2.5h。
  27. 如权利要求23所述的方法，所述步骤A)中，离子交换反应后且静止陈化之前包括：将反应液进行过滤，采用低沸点有机溶剂对滤液进行溶剂置换。
  28. 如权利要求27所述的方法，所述步骤A)原料中所述低沸点溶剂包括乙醇、戊烷、乙醚、丙酮和二氯甲烷中的至少一种。
  29. 如权利要求27所述的方法，所述步骤A)中溶剂置换之后且静止陈化之前包括：采用氮硅烷进行改性处理；优选地，改性处理的反应温度为500-800℃，反应时间为1-60min。
  30. 如权利要求29所述的方法，所述步骤A)中所述氮硅烷包括六甲基二氮硅烷、叠氮基三甲基硅烷和六甲基环三硅氮烷中的至少一种。
  31. 一种改进的二氧化硅气凝胶制备方法，其特征在于，包括以下步骤：
    A)使用阳离子交换树脂和硅酸盐溶液作为原料进行混合；
    B)将混合后的物质静置，得到气凝胶前驱体；
    C)将气凝胶前驱体进行干燥，干燥后制得二氧化硅气凝胶。
  32. 如权利要求31所述的方法，所述步骤A)中，所述硅酸钠溶液的浓度不超过4.5mol/L。
  33. 如权利要求31所述的方法，所述步骤A)中所述硅酸钠溶液中硅酸钠与所述阳离子交换树脂粉体的质量比值不超过100。
  34. 如权利要求31所述的方法，所述步骤A)中离子交换反应于搅拌条件下进行，反应温度为25-90℃，反应时间为1.5-2.5h。
  35. 如权利要求31所述的方法，所述步骤B)中离子交换反应后且静止陈化之前包括：将反应液进行过滤，采用低沸点有机溶剂对滤液进行溶剂置换。
  36. 如权利要求35所述的方法，所述步骤B)所述低沸点溶剂包括乙醇、戊烷、乙醚、丙酮和二氯甲烷中的至少一种。
  37. 如权利要求35所述的方法，所述步骤B)，溶剂置换之后且静止陈化之前包括：采用氮硅烷进行改性处理；优选地，改性处理的反应温度为500-800℃，反应时间为1-60min。
  38. 如权利要求37所述的方法，所述步骤B)，所述氮硅烷包括六甲基二氮硅烷、叠氮基三甲基硅烷和六甲基环三硅氮烷中的至少一种。
  39. 如权利要求37所述的方法，所述步骤C)中干燥采用常温自然干燥、微波干燥或高温无氧干燥中的任一种。
  40. 一种二氧化硅气凝胶，其特征在于，由权利要求1-39任一项所述的二氧化硅气凝胶的制备方法制得，所述二氧化硅气凝胶为多孔结构。
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