Abstract
Hybrid xerogels RF/Si were synthesized by controlling the chemical variables involved in the polymerization process (i.e., molar ratios, dilution ratio, catalysts, etc.) and evaluated as insulator materials. Higher insulating performances were recorded for these hybrids compared with their counterparts made from only one of their components (i.e., RF or Si xerogels with similar porous characteristics). The analysis of chemical and structural features correlated with heat transfer methods was useful in understanding the sum of contributions involved in the thermal conductivity of RF/Si xerogels. Variables such as roughness and tortuosity can be used to improve the performance of xerogels from a different perspective. In this way, thermal conductivities of 25 mW/mK were achieved without lengthy process steps or special drying methods. Knowledge of material design and the use of microwave heating during the synthesis allowed us to approach a simple and cost-effective process. These results suggest that the hybrid materials developed in this work are a good starting point for the future of the massive production of insulation materials.
Highlights
The global situation regarding climate change and the depletion of resources used as the main source of energy has brought as a consequence new concepts in the generation and in the consumption of energy
Non-hybrid resorcinol– formaldehyde (RF) and Si xerogels were prepared for comparison. These materials corresponded to the limits of 0% and 100% of Si content, respectively. These non-hybrid xerogels were synthesized selecting the appropriate concentration of reagents to achieve envelope densities and pore sizes comparable with those obtained for the hybrid RF/Si xerogels
For hybrid xerogels synthesized by microwave heating, the initial drying performed under microwave heating resulted in a slight collapse, and less pore volume and smaller pore size
Summary
The global situation regarding climate change and the depletion of resources used as the main source of energy has brought as a consequence new concepts in the generation and in the consumption of energy. The small pore sizes of these aerogels allow nullification of the convection and gas conductivity, so only radiation and solid conductivity contribute to the heat transfer process [8,15] These materials reach thermal conductivities around 10–20 mW/mK and have a wide variety of applications [9,13]. This work proposes a cost-effective synthesis route for obtaining hybrid xerogels with suitable characteristics to perform as insulators To achieve this goal, hybrid RF/Si materials were synthesized through a sol–gel process assisted by microwave (MW) heating, followed by ambient pressure drying and using AEAPTMES as a catalyst. 96%), 3-[2-aminoethylamino]propyl]trimethoxysilane (AEAPTMES, Sigma Aldrich 97%), ammonia 2M (Acros Organics, 25%), ammonium fluoride 0.05 M (HN4F, Sigma-Aldrich 98%) and NaOH (VWR, 99%)
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