Aerogel
Aerogel is a synthetic, porous ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and low thermal conductivity. It is considered to be the most low-density solid material and has several unique physical properties (e.g., as thermal insulation).
Aerogel was first created by an American chemist, Samuel Stephens Kistler (1900-1975) in 1931, as the result of a bet with Charles Learned over who could replace the liquid in jellies with gas without causing shrinkage. The first aerogels were produced from silica gels. Since then it has been proven that aerogels can be prepared from a number of different materials like alumina, chrome, tin dioxide and carbon. The synthesis of (silica) aerogels may be divided into three general steps: preparation of the gel by sol–gel processes, ageing of the gel in its mother solution to prevent the gel from shrinking during drying, and drying the gel under special conditions to prevent the gel structure from collapsing.
Aerogel insulations were developed in the 1980s by Aspen Aerogels, which is a spin-off venture of the National Aeronautics and Space Administration (NASA). The real breakthrough occurred around the year 2000, when reinforcing fibres were successfully mixed into the material. The result was a flexible building material with good technical parameters, which is widely applicable in the building industry. Admittedly, it was applied in powder form previously as insulation for large roof windows and other transparent building structures.
Silica aerogel is a dendritic network of loose silicon. It is prepared by carefully removing the liquid part from silica alcogel and replacing it with gas, thereby producing the final product containing 99.8% air. It has low thermal conductivity and good physical and mechanical properties. It does not age or get mouldy, and environmental problems should not be taken into account during its application. It is hydrophobic (water repellent), water permeable, environmentally safe, and fully recyclable. Its excellent thermal insulation quality is caused by one-dimensional molecular chain. Air cannot circulate in the pore system of aerogels, so all forms of heat transport are limited.
Thermal conduction slowly occurs inside the nanostructure because of the small interfaces between the aerogel particles. In addition, the pores are smaller than the length of the path required by the internal gas molecules for free collisions. They interfere with cellular walls rather than with each other, so any convective heat transport is minimal. The size of the nanopores is also smaller than the wavelength of infrared rays; therefore, the nanocellular walls reflect and dissolve a significant part of the heat rays.
Aerogel is also used as nanoporous translucent glass (e.g., NANOGEL®). It is preferably used as a thermal insulating window (e.g., curtain walls), skylight window, transparent partition wall, or balcony railing element.
Aerogel is especially very interesting as a translucent or transparent insulation material because of its combination of low thermal conductivity and high transmittance of daylight and solar energy. Two types of highly insulating windows were developed for this purpose based on a granular aerogel and a monolithic aerogel.
Granular aerogel-based windows were developed by ZAE Bayern (Germany). They produce two types of granular aerogel, i.e., semitransparent and highly translucent granulates. This granular aerogel is stacked in a 16 mm wide polymethyl-methacrylate (PMMA) doubleskin sheet between two gaps (i.e., either 12 or 16 mm in width and respectively filled with krypton or argon) and glass panes. Monolithic aerogel-based windows were developed by the HILIT+ project of the European Union. This window is produced in combination with the technology of vacuum glazing by applying a pressure between 1 and 10 m bar.
source : https://doaj.org/toc/1210-3896
Aerogel is a synthetic, porous ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and low thermal conductivity. It is considered to be the most low-density solid material and has several unique physical properties (e.g., as thermal insulation).
Aerogel was first created by an American chemist, Samuel Stephens Kistler (1900-1975) in 1931, as the result of a bet with Charles Learned over who could replace the liquid in jellies with gas without causing shrinkage. The first aerogels were produced from silica gels. Since then it has been proven that aerogels can be prepared from a number of different materials like alumina, chrome, tin dioxide and carbon. The synthesis of (silica) aerogels may be divided into three general steps: preparation of the gel by sol–gel processes, ageing of the gel in its mother solution to prevent the gel from shrinking during drying, and drying the gel under special conditions to prevent the gel structure from collapsing.
Aerogel insulations were developed in the 1980s by Aspen Aerogels, which is a spin-off venture of the National Aeronautics and Space Administration (NASA). The real breakthrough occurred around the year 2000, when reinforcing fibres were successfully mixed into the material. The result was a flexible building material with good technical parameters, which is widely applicable in the building industry. Admittedly, it was applied in powder form previously as insulation for large roof windows and other transparent building structures.
Silica aerogel is a dendritic network of loose silicon. It is prepared by carefully removing the liquid part from silica alcogel and replacing it with gas, thereby producing the final product containing 99.8% air. It has low thermal conductivity and good physical and mechanical properties. It does not age or get mouldy, and environmental problems should not be taken into account during its application. It is hydrophobic (water repellent), water permeable, environmentally safe, and fully recyclable. Its excellent thermal insulation quality is caused by one-dimensional molecular chain. Air cannot circulate in the pore system of aerogels, so all forms of heat transport are limited.
Thermal conduction slowly occurs inside the nanostructure because of the small interfaces between the aerogel particles. In addition, the pores are smaller than the length of the path required by the internal gas molecules for free collisions. They interfere with cellular walls rather than with each other, so any convective heat transport is minimal. The size of the nanopores is also smaller than the wavelength of infrared rays; therefore, the nanocellular walls reflect and dissolve a significant part of the heat rays.
Aerogel is also used as nanoporous translucent glass (e.g., NANOGEL®). It is preferably used as a thermal insulating window (e.g., curtain walls), skylight window, transparent partition wall, or balcony railing element.
Aerogel is especially very interesting as a translucent or transparent insulation material because of its combination of low thermal conductivity and high transmittance of daylight and solar energy. Two types of highly insulating windows were developed for this purpose based on a granular aerogel and a monolithic aerogel.
Granular aerogel-based windows were developed by ZAE Bayern (Germany). They produce two types of granular aerogel, i.e., semitransparent and highly translucent granulates. This granular aerogel is stacked in a 16 mm wide polymethyl-methacrylate (PMMA) doubleskin sheet between two gaps (i.e., either 12 or 16 mm in width and respectively filled with krypton or argon) and glass panes. Monolithic aerogel-based windows were developed by the HILIT+ project of the European Union. This window is produced in combination with the technology of vacuum glazing by applying a pressure between 1 and 10 m bar.
source : https://doaj.org/toc/1210-3896
Civil Scholar is a Blog by Aravind Samala on Construction, Environment, Technology, Trends and Innovation.