When talking about the "ghost" of materials science, aerogel must be mentioned! It's a true "hexagonal warrior" in the materials world, with extremely low density but astonishing performance.
How light is it? In fact, it has extremely high porosity yet very low thermal conductivity. This is because the pore size of its nanopores is smaller than the mean free path of molecules in ammonia and oxygen, the main components of air. Therefore, air convection is difficult to occur, thus inhibiting the conduction of heat by gas molecules. At the same time, the small contact surface of particles in nanoporous materials also limits solid-state heat conduction. Simply put, it's the thermal insulation performance derived from its porous structure.
This superior thermal insulation capability has been widely used in the defense industry. Using it as a thermal insulation material for aero engines not only provides excellent thermal insulation but also reduces engine weight.
It also has many other impressive properties, such as good insulation, flame retardancy, and sound insulation. It shines in fields such as construction, electronics, and chemicals.
So how exactly is this amazing aerogel formed? It's actually prepared by the coagulation of a liquid colloid (liquid sol).
The preparation process is quite interesting. If certain conditions are controlled during the coagulation of the liquid sol to form a gel, nanoclusters with different structures can be formed. These clusters adhere to each other, forming a gel. The solid framework of the gel is surrounded by the remaining liquid reagents from the reaction.
Next, this gel is placed in a high-pressure container and pressurized and heated, causing a phase transition of the liquid within the gel, forming a supercritical fluid. Slowly extracting the supercritical fluid allows the gel's network structure to remain intact, thus obtaining the aerogel.