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首页> 外文期刊>Journal of Non-Crystalline Solids: A Journal Devoted to Oxide, Halide, Chalcogenide and Metallic Glasses, Amorphous Semiconductors, Non-Crystalline Films, Glass-Ceramics and Glassy Composites >Effect of drying on properties of silica gel
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Effect of drying on properties of silica gel

机译：干燥对硅胶性能的影响

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Viscoelastic properties and permeability of a silica gel have been followed during the course of drying. The modulus and viscosity of the network rise by several orders of magnitude, and exhibit power-law dependence on the density of the gel. An aerogel was prepared from an undried gel, and its modulus was found by hydrostatic compression in a mercury porosimeter. Pore size distribution of the aerogel was determined by nitrogen sorption before and after compression. The bulk modulus of the aerogel was very close to that of the wet gel at low densities, but at higher densities the wet gels were more rigid that the compressed aerogels. This difference is attributed to aging of the wet gels in the pore liquid (water). The final shrinkage of the wet gels was greater than expected, based on the viscoelastic properties and the calculated capillary pressure, and the difference is attributed to accelerated viscoelastic relaxation of the network under high capillary stresses. The permeability decreases by almost four orders of magnitude as the gel contracts and pore size inferred from the permeability (r(w)) decreases in direct proportion to the pore volume. The pore size measured by nitrogen desorption (r(BT)) agrees closely with r(w), as expected on theoretical grounds. For compliant aerogels, the nitrogen desorption process causes substantial compression of the gel, because of the capillary pressure exerted by liquid nitrogen. In such cases, the true pore size and pore volume can be estimated, given knowledge of the elastic modulus of the network; the corrected value of r(BT) agrees well with r(W). At high densities r(W) was about 0.5 nm smaller than r(BT), and this discrepancy is probably caused by neglect of the existence of a relatively immobile layer of water of that thickness on the surface of the network. (C) 1997 Elsevier Science B.V.
机译：在干燥过程中遵循了硅胶的粘弹性和渗透性。网络的模量和粘度上升了几个数量级，并且表现出对凝胶密度的幂律依赖性。由未干燥的凝胶制备气凝胶，并通过在水银孔隙率计中的静水压缩发现其模量。通过压缩之前和之后的氮吸附来确定气凝胶的孔径分布。在低密度下，气凝胶的体积模量非常接近于湿凝胶的体积模量，但是在较高密度下，与压缩气凝胶相比，湿凝胶的刚性更高。这种差异归因于孔隙液体（水）中湿凝胶的老化。基于粘弹性和计算出的毛细压力，湿凝胶的最终收缩比预期的要大，并且差异归因于在高毛细应力下网络的加速粘弹性松弛。当凝胶收缩时，渗透率降低了几乎四个数量级，并且从渗透率（r（w））推断出的孔径与孔体积成正比地降低。正如理论上所预期的那样，通过氮脱附测量的孔径（r（BT））与r（w）非常吻合。对于顺应性气凝胶，由于液氮施加的毛细压力，氮的解吸过程会导致凝胶的显着压缩。在这种情况下，只要知道网络的弹性模量，就可以估算出真正的孔径和孔体积。 r（BT）的校正值与r（W）非常吻合。在高密度下，r（W）比r（BT）小约0.5 nm，并且这种差异可能是由于忽略了网络表面上该厚度的相对固定的水层的存在而引起的。 （C）1997年Elsevier Science B.V.

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