热处理对粉煤灰酸渣基二氧化硅气凝胶结构和疏水性的影响

粉煤灰酸渣是粉煤灰经酸溶提铝后的副产品,主要化学成分为无定形二氧化硅,其资源化利用不仅解决了粉煤灰酸渣堆存带来的环境问题,还能获得附加值较高的二氧化硅气凝胶。以粉煤灰酸渣制备的水玻璃为原料,通过溶胶-凝胶—溶剂交换/表面改性—常压干燥工艺成功制备了低密度（0.083 g/cm³）、高比表面积（708 m²/g）、高疏水性（接触角为143°）的多孔二氧化硅气凝胶。通过热重-差热分析、红外光谱分析、接触角测试、扫描电镜分析、氮气吸附-脱附测试等手段对热处理前后二氧化硅气凝胶的结构和疏水性进行了表征。结果表明,随着热处理温度升高,二氧化硅气凝胶的比表面积增大、疏水性逐渐减弱直至消失。300 ℃热处理后,二氧化硅气凝胶仍具有较强的疏水性（接触角约为128°）,密度为0.080 g/cm³。当热处温度为400~600 ℃时,二氧化硅气凝胶仍具有中孔结构,由疏水性变为亲水性,密度从0.073 g/cm³增加到0.078 g/cm³。

Effect of thermal treatment on structure and hydrophobicity of SiO2 aerogels derived from fly ash acid sludge

Fly ash acid sludge is by-product of fly ash after alumina extraction by acid leaching process,and its main compo-nent is amorphous silica.Its resource utilization not only solves the environmental problems caused by the accumulation of fly ash acid sludge,but also can obtain silica aerogels with high added value.SiO2 aerogels with mesoporous structure represented a low density of 0.083 g/cm³,high surface area of 708 m²/g and high hydrophobicity(contact angle of 143°)were prepared by sol-gel method,solvent exchange/surface modification and atmospheric drying using the sodium silicate derived from fly ash acid sludge.The structure and hydrophobicity of SiO2 aerogels before and after heat treatment were characterized by thermogravimetric analyzer,fourier transform infrared spectrometer,contact angle tester,scanning electron microscope and N2 adsorption-desorption test.The experimental results indicated that with the increase of heat treatment temperature,the specific surface area of SiO2 aerogels increased,and the hydrophobicity gradually decreased until it disappeared.When the heating temperature reached to 300℃,the hydrophobicity of silica aerogels remained unchanged(contact angle of 128°),and their den-sity was 0.080 g/cm³.After heating temperature was ranged from 400℃to 600℃,the surface characteristic of silica aerogels with the mesoporous structure became hydrophilic and the density of silica aerogels increased from 0.073 to 0.078 g/cm³.