CN102515182A - Method for preparing SiO2 airgel by compounding fly ash and diatomite - Google Patents

Abstract

The invention provides a method for preparing _SiO2 airgel by compounding fly ash and diatomite, which includes medium-temperature mechanical activation of fly ash and diatomite, preparation of _SiO2 sol, preparation of wet gel, aging of mother liquor, and one-step solvent exchange After six steps of surface modification and normal pressure drying, the SiO ₂ airgel obtained is similar to that of the airgel material with water glass as the silicon source, because fly ash and diatomite are used as the cheap silicon source and the common The pressure drying process greatly reduces the production cost, making it have a wider application prospect in the fields of building materials, thermal insulation, and environmental protection adsorption.

Description

Method for preparing SiO2 airgel by compounding fly ash and diatomite

technical field

The invention relates to a method for preparing _SiO2 airgel material by compounding fly ash and diatomite, which belongs to the field of functional material preparation.

Background technique

SiO ₂ airgel is a new type of amorphous solid-state material composed of nanometer-scale particles and air as the dispersion medium. 0.01～0.2g/cm ³ ), large specific surface area (up to 800～1000m ² /g), high porosity (up to 80%～99.8%), low thermal conductivity (single particle airgel at room temperature: 0.013 ~0.02W/m·K, airgel particle accumulation: 0.4W/m ² ·K) and other characteristics, it is widely used in thermal insulation materials, optics, acoustics, electricity, catalysis, drug carriers, adsorption materials and other fields prospect. However, due to the sharp increase in thermal conductivity of silica airgel materials at high temperatures, its application in thermal insulation materials is largely limited. In addition, since airgel is composed of nanometer-sized _SiO2 It is piled up and has a large porosity, so its strength is very low and its brittleness is relatively high, which greatly limits its application in various fields. The existing silicon sources for preparing airgel mainly include: organosilicon compounds such as ethyl orthosilicate, polyethoxydisiloxane, methyltrimethoxysilane, and silicon tetrachloride. The present invention uses cheap fly ash Combining with diatomaceous earth as a silicon source greatly reduces the production cost of airgel.

Contents of the invention

In order to overcome the disadvantages of high preparation cost and long production cycle of existing airgel materials, the present invention provides a low-cost method for preparing silicon airgel materials. The core content of this preparation method is to use high-quality fly ash and diatomaceous earth as a silicon source to prepare _SiO2 airgel materials through a series of processes. The reaction conditions of this preparation process are easy to achieve, and the production cycle is short and the cost is low. , the basic performance index of the obtained SiO ₂ airgel reaches the technical performance index of the existing SiO ₂ airgel prepared with industrial water glass as the silicon source.

The SiO ₂ airgel material preparation process that the fly ash and diatomite composite make of the present invention comprises fly ash and diatom earth raw material mechanical activation treatment, SiO _sol preparation, wet gel preparation, aging, One-step solvent exchange/surface modification, six steps of normal pressure drying. Described SiO _sol preparation has adopted following process:

A. Use fly ash and diatomite as raw materials, mix them according to a certain mass ratio after activation at a certain temperature for a period of time; the temperature is 300-800°C, and the time is 10min-90min, and the specific ratio refers to the mass ratio , the optimum mass ratio of fly ash to diatomaceous earth is between 1:2 and 3:1. the

B. Mix reaction with the solution alkali of certain concentration for a period of time at a certain temperature in a certain proportion, carry out suction filtration to the mixture after the reaction, dilute the filtrate with distilled water in a certain proportion, superacid type cation exchange resin; described reaction temperature is the most The optimal value is 70-120°C, the alkali concentration is between 5%-20%, the optimal value of the reaction time is between 0.5h-6h; the optimal value of the dilution ratio of the filtrate and distilled water is 1:0.5-1: between 5;

C. After it gels under natural conditions, it is immersed in an organic solvent solution for aging, and the aged gel is immersed in a certain proportion of ethanol/trimethylchlorosilane/n-hexane mixed solution, so that the solvent exchange surface modification can be done in one step. Finally, dry the modified organogel at normal temperature and pressure for a period of time to obtain the SiO ₂ airgel material. The molar ratio of ethanol to trimethylchlorosilane in the mixed solution is 1:0.5 to 1:3, and the drying time is 2 to 6 hours at 40°C to 60°C, and 1 hour at 80°C to 150°C. ~3h.

The base may be selected from: sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, ammonia water and the like. the

The organic solvent may be selected from: methanol, ethanol, propanol, tert-butanol and the like. the

The performance of the airgel material prepared by compounding fly ash and diatomaceous earth is similar to that of the airgel prepared by using water glass as the silicon source, and the production process is simple, the production cost is reduced, and it can be widely used in thermal insulation materials , environmental protection adsorption materials, etc., are widely used in the fields of building materials, aerospace, environmental protection and so on. the

Description of drawings

Fig. 1 is the photo of the SiO ₂ aerogel obtained by low-cost normal pressure drying of the present invention.

Fig. 2 is the process flow diagram of the _SiO2 airgel obtained by low-cost atmospheric pressure drying of the present invention.

Detailed ways

Embodiments of the present invention will be described in detail below in conjunction with technical solutions and accompanying drawings. the

Example 1

50g of fly ash was activated in a muffle furnace at 800°C for 60min; 50g of diatomite was roasted in a muffle furnace at 600°C for 3h, mixed with fly ash and added to 500mL of 10% NaOH solution at 80°C Reaction at low temperature for 150min, filter to take the filtrate, dilute with distilled water at a ratio of 1:1, pass through a cationic resin, control the pH to 2-3, titrate with ammonia water to pH=5.5, age the obtained hydrogel at 30°C, and then wash with ethanol , n-hexane, and trimethylchlorosilane for solvent exchange/surface modification, the molar ratio of ethanol to trimethylchlorosilane is 2:3, the volume ratio of trimethylchlorosilane to wet gel is 1:1, and the time is 24h . Then dry it in an oven at 80°C for 2 hours, and then dry it at 150°C for 1 hour to obtain SiO ₂ airgel with a specific surface area of 531.7m ² /g, a density of 0.129g/cm ³ , and an average pore diameter of the internal micropores. 25nm.

Example 2

70g of fly ash, 50g of diatomaceous earth, activated in a muffle furnace at 700°C for 70min; In a 15% NaOH solution, react at 90°C for 120 minutes, filter the filtrate, dilute it with distilled water at a ratio of 1:2, pass through a cationic resin, control the pH to 2-3, and titrate with ammonia water to pH = 6.0, and the obtained water coagulates The gel was aged at 30°C, and then solvent exchange/surface modification was carried out with ethanol, n-hexane, and trimethylchlorosilane. The molar ratio of ethanol to trimethylchlorosilane was 1:1, and trimethylchlorosilane and wet gel The volume ratio is 1:1.5, and the time is 48h. Then dry it in an oven at 80°C for 4 hours, and dry it at 150°C for 1 hour to obtain SiO ₂ airgel with a specific surface area of 548.4m ² /g and a density of 0.105g/cm ³ 18nm.

Claims (3)

1. flyash and the compound preparation SiO of zeyssatite ₂The gas gel method is characterized in that,

A. be raw material with flyash and zeyssatite, after 300～800 ℃ of following activation, mix that the time is 10min～90min; Flyash and zeyssatite blended mass ratio are between 1: 2～3: 1;

B. in proportion 70～120 ℃ of following and alkaline solution hybrid reactions, carry out suction filtration, filtrating is diluted, cross strongly acidic cation-exchange with zero(ppm) water to reacting the back mixture; The concentration of alkaline solution is that the reaction times is between 0.5h～6h between 5%～20%; Said filtrating and distilled water diluting ratio are between 1: 0.5～1: 5;

C. it is aging to treat that it immerses behind gel in the organic solvent solution under field conditions (factors); Gel after aging is immersed in ethanol/trimethylchlorosilane/normal hexane mixing solutions; Make the solvent exchange surface-treated in a step, accomplish; At last the organogel after the modification is carried out drying for some time at normal temperatures and pressures, promptly get SiO ₂Aerogel material; Ethanol and trimethylchlorosilane mol ratio are between 1: 0.5～1: 3 in the mixing solutions; Be 40 ℃～60 ℃ down dry 2～6h time of drying, 80 ℃～150 ℃ down dry 1～3h.

2. a kind of flyash according to claim 1 and the compound preparation SiO2 of zeyssatite gas gel method is characterized in that said alkali is selected from sodium hydroxide, Pottasium Hydroxide, yellow soda ash, salt of wormwood, sodium hydrogencarbonate, saleratus, ammoniacal liquor.

3. a kind of flyash according to claim 1 and the compound preparation SiO2 of zeyssatite gas gel method is characterized in that said organic solvent is selected from methyl alcohol, ethanol, propyl alcohol, the trimethyl carbinol.

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