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Electrochemical Sensors/Biosensors Based on Carbon Aerogels/Xerogels
Published in Mahmood Aliofkhazraei, Advances in Nanostructured Composites, 2019
Liana Maria Muresan, Aglaia Raluca Deac
The first method used to prepare aerogels was supercritical drying. This method consists in drying assisted by the use of supercritical fluids, usually CO2, leading to preservation of the high open porosity and superior textural properties of the wet gel in its dry form. Supercritical drying has major advantages in comparison with classical drying methods, avoiding the presence of vapor-liquid intermediates and surface tensions in the gel pores and thus preventing pore collapse phenomenon (García-González et al. 2012). Nevertheless, supercritical drying does not always preserve the wet gel structure (Job et al. 2005). The experimental conditions (pH, ratio of precursors, etc.) should be carefully chosen in order to avoid shrinkage and residual surface tensions.
Fabrication Techniques for Capacitive Silicon Resonators
Published in Nguyen Van Toan, Takahito Ono, Capacitive Silicon Resonators, 2019
Supercritical drying is a process to remove liquid in a precisely controlled way without severe deformation and collapse of structure. The primary cause of such damage is the effect of surface tension. The specimen is subject to considerable forces, which are present at the phase boundary as the liquid evaporates. The most common specimen medium, water, has a high surface tension to air, by comparison to that for acetone, which is considerably lower. However, after wet processing (such as release), a specimen dried by supercritical drying is unaffected by any surface tension, thus preventing stiction. The common transitional method is liquefied CO2 due to its low critical temperature and the associated critical pressure. For this reason, the supercritical CO2 has extremely low surface tension, and as a result does not pull structures down as it transitions from liquid to gas. The supercritical dryer machine is introduced in Figure 3.18.
Different Fabrication Techniques of Aerogels and Its Applications
Published in Sajith Thottathil, Sabu Thomas, Nandakumar Kalarikkal, Didier Rouxel, Advanced Polymeric Materials for Sustainability and Innovations, 2018
Fathima Parveen, Raghvendra Kumar Mishra
Supercritical drying techniques are generally expensive on a large scale. So, the research is being carried out to find alternative ways to reduce the production cost, increase the mechanical integrity, and reduce the shrinkage.
Intensification methods of supercritical drying for aerogels production
Published in Drying Technology, 2020
Natalia Menshutina, Pavel Tsygankov, Illarion Khudeev, Artem Lebedev
The process of supercritical drying, after the apparatus is closed, can be divided into the following stages: pressurization (including spillage), displacement of the solvent from the free volume of the apparatus, and diffusion substitution of the solvent in the pores of the gel with the supercritical carbon dioxide. Convective transport determines the rate of solvent displacement from the free volume of the apparatus. The diffusion process determines the rate of substitution of the solvent in the pores of the gel.