A kind of preparation method of atmospheric pressure silica airgel using nitrate

Abstract

The invention provides a normal pressure preparation scheme of aerosil by using nitrate. The preparation scheme comprises the following steps: a certain mass fraction of potassium nitrate or a sodium nitrate salting liquid is used for immersing aged silica wet gel, and immersed wet gel is obtained; immersed wet gel is placed in a certain environment, in order to precipitate nitrate; after solvent replacement is carried out for the gel by using an organic solvent with low surface tension, the gel is dried at a normal pressure, and the aerosil is obtained. Compared with the prior art, the normal pressure preparation method of aerosol is improved based on the normal pressure preparation method of the aerogel, nitrate is employed for wrapping the aged aerogel, and the aerosil product with good performance parameters is prepared. In addition, the normal pressure preparation scheme of aerosil can reduce cost, and is good for industrial production.

Description

technical field [0001] The invention relates to the field of preparation of porous nanomaterial silicon dioxide airgel, in particular to a preparation method of atmospheric pressure silicon dioxide airgel using nitrate. Background technique [0002] The existing silica airgel preparation mainly includes two processes of sol-gel synthesis and post-treatment. [0003] Sol-gel synthesis refers to the hydrolysis and water / alcohol polycondensation of precursors under certain conditions to synthesize wet gels, and the post-treatment process includes aging and drying. [0004] Aging means that after the gel is formed, the monomers or small gel clusters in the solution phase continue to stick together and connect with the network, so that the formed gel network is cross-linked and gradually becomes thicker, strengthening the sol-gel The mechanical properties of the fragile solid skeleton formed in the process, in order to resist the drying stress, most of the existing processes soa...

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Problems solved by technology

[0010] The disadvantages of supercritical drying preparation are mainly time-consuming, high cost, and certain operational difficulty and danger: the airgel permeability is low, which leads to the slowdown of carbon dioxide replacement and pressure relief steps in the kettle, so that the drying time needs to reach 50 ~70 hours, which greatly affects the process of industrial production; the basic organic silicon source used in the supercritical drying method is expensive and has certain toxicity; the core equipment of the supercritical drying technology is an autoclave, and the equipment system is relatively complicated. For critical drying technology, the required working pressure is as high as 7-20MPa, which will have a negative impact on equipment, cost, operation technology and safety, especially prone to equipment explosion, and the energy consumption and maintenance costs required for operation are also high

[0011] The disadvantages of atmospheric drying preparation are mainly that the finished product parameters are low and the overall process takes a long time: after the airgel aging is completed, there are still silanol groups on the surface of the gel pores that have not participated in the reaction. Reagents are used to react the remaining silanol groups to avoid irreversible shrinkage of the airgel network structure due to mutual combination; at the same time, liquids with low surface tensions should be used to replace the original liquids with high surface tensions to reduce the shrinkage during the drying process stress

The time required for these steps is often longer, and because normal pressure drying cannot solve the impact of the removal of solvent (liquid phase) (i.e. drying process) on the gel skeleton (solid phase), the gel network will inevitably appear in the preparation process. Irreversible shrinkage phenomenon, so its finished product parameters are often more general

[0012] In general, supercritical drying is greatly affected by industrial development because of its high equipment requirements (commonly used CO2 supercritical requires 80atm), high maintenance costs and long total drying time (affected by low airgel permeability). limit

Compared with supercritical drying, the equipment cost of atmospheric drying is lower, and its source of silicon is wider (supercritical drying is often an organic silicon source, and atmospheric drying can be an inorganic silicon source such as water glass or an organic silicon source), However, drying at atmospheric pressure requires lengthy solvent exchange treatment to reduce the capillary pressure acting on the nanostructure of silica airgel or increase its skeleton strength to resist these forces. The process requirements are higher, the preparation cycle is longer and the product parameters are relatively low generally

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