| SiO2 aerogels were first prepared by S.S.Kistler in the early 1930s and have attracted much attention because of their low density and low thermal conductivity properties.SiO2 aerogels are widely used in insulation,catalytic degradation,biosensors and electrochemistry and so on.However,the thermal conductivity of SiO2 aerogels with different sizes are very different,and the synthesis conditions have great influence on the final structure size of SiO2 aerogels.Therefore,it is of great significance to study the preparation of SiO2 aerogels that meet the required structural dimensions.We had prepared SiO2 aerogels by sol-gel method.The effects of the amount of ethanol,the amount of water,the pH value of the gel and the concentration of the modified solution on the thermal conductivity of the SiO2 aerogels were investigated in the whole preparation process.The SiO2 aerogels with low thermal conductivity were prepared,and the self-made SiO2 aerogels was treated as an insulating filler to prepare the water-based thermal insulation coating.The effects of the amount of additives and the amount of the insulation filler on the performance of the prepared coating were discussed.The synthesized of water-based insulation coating not only meet environmental requirements,but also achieve the effect of thermal insulation.The specific research contents are as follows:1?SiO2 aerogels were synthesized by sol-gel method,the change of the amount of ethanol in the reaction process has a great influence on the thermal conductivity of the aerogels,which mainly affects the structural size of the gel,so as to further affects the thermal conductivity of the aerogels.With the increase of the dosage of ethanol,the thermal conductivity decreased first.When the lowest point is reached,the thermal conductivity increases as the amount of ethanol is increased.When the molar ratio of ethanol to ethyl orthosilicate was 20,the minimum thermal conductivity of aerogels was 0.0217 W/(m k).Water controlled the reaction limit,which worked as a reactant involved in the hydrolysis of ethyl orthosilicate and the product of gel polycondensa-tion.So the appropriate dosage or content of water can could make the silicic acid hydrolysis-condensation reaction carried out more thoroughly.When the gel was formed,[the gel rate also accelerated with the increase of pH value,which led to the dense structure and smaller pore size of the as-prepared SiO2 aerogels,and thermal conductivity also showed an upward trend.On the basis of gel time and thermal conductivity and other factors,the final determination of the best gel pH value is 6.5 or so.In order to dry at room temperature and pressure,reduce the capillary force,so that the aerogels network structure as far as possible to retain integrity.We have the hydrophobicity modification of the wet gel.With the increase of the concentration of the modifier,the better the modification effect is,the more contact angle is,the more complete the aerogels structure is,the thermal conductivity is also decreasing,which is favorable for the preparation of low thermal conductivity of SiO2 aerogels.2?In the self-made hydrophobic SiO2 aerogels pretreatment process,we investigated the effect of the hydrophilic agent(KH550)and the high temperature treatment on the aerogels modification.The results show that the high temperature treatment of this method is simple,and the effect is better.When the treatment temperature reaches 260 ?,both the hydrophilic effect and thermal conductivity of aerogels can meet the experimental requirements.And then in the water-based insulation coating preparation process with the use of the heat-treated SiO2 aerogels,we investigated the effects of the dosages of dispersant,wetting agent and SiO2 aerogels on the thermal insulation properties of the coatings.The results show that when the amount of dispersant is 2.5g,the amount of wetting agent is 1g and the amount of SiO2 aerogels is 30%,the thermal conductivity of the coating is the lowest,and the thermal insulation effect is better. |
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