A highly transparent silica-based insulating material that can generate high temperatures in sunlight, even in cold winter conditions.

Aerogels are contradictory materials. So fleeting that they hardly seem to be there, but they have extraordinary properties. The MIT team, working with engineers from different specialties, has developed a material that they believe is capable of transmitting sunlight while effectively trapping solar heat.

In an article published in the ACS Nano Magazine, Evelyn Wang, head of the mechanical engineering department, graduate student Lin Zhao, energy engineering professor Gang Chen, and their colleagues describe how they created the airgel by controlling the hydrolysis and condensation rates of orthosilicate tetramethyl (TMOS). They discovered a new process for doing this, which they claim not only improves the optical transparency of the material, but also cuts the manufacturing time from weeks to days.

The key to making it work is in the precise proportions of the different materials from which the airgel has been synthesized, the article explains. The process involves mixing a catalyst with grains of a silica-containing compound in a liquid solution, then drying the resulting gel to leave a matrix that is mostly air but retains the mechanical strength of the original mixture. . Producing a mixture that dries much faster than conventional hydrogel precursors produced a gel with a much smaller pore size between its grains, resulting in less light scattering.

According to Wang, conventional hydrogels, although very effective insulators, transmit a maximum of 70% of incident light. The new airgel, however, allows 95% of the incident sunlight to pass through, but retains the highly insulating properties, which means that the heat from the sunlight does not escape.

The team tested the material on a sunny day in the middle of winter, which in Cambridge, Mass. Tends to be well below 0 ° C. They built a passive device consisting of a dark heat-absorbing material covered with a layer of the new airgel. The dark material reached and maintained a temperature of 220 ° C, they report.

Previously, these temperatures were only obtained from sunlight by a system of concentrating mirrors and lenses that focused sunlight on a central line or point. These systems are more complex and more expensive than the combination airgel-passive collector.

The temperature reached would be suitable for producing domestic hot water in a roofing system, for supplying air conditioning systems, or for a wide variety of applications in chemical or food manufacturing that offer many manufacturing processes, suggests. the team.

More information: news.mit.edu