Preparation And Property Study Of Carbon-Doped Silica Aerogels

Silica aerogel is a kind of amorphous solid material with three-dimensional network skeleton structure.It has many excellent properties with high specific surface area,high porosity,low density and low thermal conductivity.These unique properties make it have a wide application and development potential,such as aerospace fields,military,petrochemical industry,industrial equipment and pipe insulation and so on.It has been reported that the radiative thermal conductivity of pure silica aerogels increases drastically with the increase of temperature,which is attributed that pure silica aerogels are infrared-transparent with the wavelength of 3-8?m.This limits the further application of aerogels in the field of thermal insulation.According to the literature,the introduction of opacifiers are generally used to further improve the thermal insulation properties of aerogel,such as Ti O₂?carbon black?Si C?Fe₃O₄?B₄C?Al₂O₃ and so on,which effectively improve the ability of aerogel to block infrared radiation to a certain extent.However,many new problems have been introduced at the same time.For example,the high density,high doping mass and thermal conductivity limited their applications.Therefore,it is an urgent problem to find a suitable opacifier.Herein,we used sol-gel method via dopping colloidal graphite and graphene into silica sol to produce composites silica aerogels.The effects of colloidal graphite and graphene on the morphology,surface area and thermal insulation properties of aerogel were investigated by means of thermophysical property test.Furthermore,theoretical analysis and estimation of thermal resistance of composite aerogels was preliminarily explored.The main content is depicted as follows:Graphite?G?-doped silica aerogels were synthesized by sol-gel method,which had three-dimensional porous structure and the specific surface area was up to¹500 m²/g.The thermal performance of graphite-doped silica aerogel was evaluated by pulse method.The results revealed that when the H₂O/Et OH/TEOS volume ratio in precursor solution was 1:4:1 and the doping amount of graphite was 0.4 wt%,the thermal conductivity of the composite aerogel was 0.017 W/?m·K?at room temperature,which lower than the thermal conductivity of pure silicaaerogelatroomtemperature?0.02W/?m·K??andeffectively improved the thermal insulation properties of aerogel.Even so,it was found that the small quantity change of doping graphite had a fluctuation on the thermal conductivity.This fluctuation was mainly ascribed to the multi-layer structure and the native thermal conductivity of graphite.Consideringthatgrapheneissingle-layerorfew-layersheets,graphene-doped silica aerogels were synthesized by sol-gel method.The unique band gap features,conjugated large?bond and layer structure of graphene sheets effectively reduced the radiation heat transfer and the thermal insulation capability of composite aerogels was enhanced?around 0.018 W/?m·K??.Especially,the numerical controllability of thermal conductivity for the graphene-doped aerogels was achieved.On the basis of experiment,the equivalent thermal resistance of carbon-doped silica composite aerogels was given by analyzing the energy distribution mechanism of the aerogel-based thermal insulation layer.It can realize the intuitive estimation to thermal insulation performance of the aerogel by controlling the parameters that affecting the thermal resistance,providing reference for practical application of composite aerogel insulation.