Airgel: one kind of science by the current limited \”material of the future.\”
Aerogels – the world\’s lightest solid material (graphene airgel Guinness recognized world\’s lightest solid) because it contained 97% air and 3% of the solid structure, only 1.5 times the density of air. In addition than very light, aerogels have a very good insulating capability, primarily because the \”Knudsen\” effect, since most of silica airgel and air composition, the thermal conductivity is generally silica solids, and very low thermal conductivity of air. Moreover, nanoporous airgel has a very level holes which allow air to pass convective heat is difficult to diffuse through the airgel. Thus aerogels often appear in the required high temperature environment, such as Mars car, on the use of the airgel to heat. In addition, water repellent airgel mainly from the modification by the surface polarity of the -OH becomes nonpolar -OR, can be obtained hydrophobic airgel. Such a \”water and fire does not invade,\” a material that looks like is the latest modern technology, in fact, aerogels in the 1930s appeared, first proposed by chemist Samuel Keith Le manufactured.
the birth of the first piece of airgel
gel material is actually very common, we like to eat jelly is a gel substance, belonging to a combination of solid and liquid. happened when Samuel child and colleague Charles Learned Take the jelly to make a bet, Charles thinks the cause gel jelly is due to its liquid nature, but Samuel child believes the gel has a solid structure, this is also the key to gel formation. In order to verify who is right, Samuel children begin the experiment proved the wet gel containing the same size and shape of a continuous solid network, the purpose of the experiment is also very simple, is to get out of the liquid gel solid structure retained, this can prove gel and liquid which is not what relationships. But easier said than done is not easy, if you simply let the liquid gel evaporates, the corresponding solid structure will inevitably shrink, because after removing the liquid molecules, they will attract each other, thereby pulling the solid structure around it start from the inside the gel will \”collapse\”, until reduced to 1/10 of the original volume. This method is certainly not Samuel child After much deliberation, onlyThere will replace the liquid inside the gel can guarantee to ensure complete solid structure. To replace it, it will definitely be a gas, because the gel has two states of matter comprising solid and liquid. But certainly not the normal gas liquid gel to replace it, so Samuel child choose Quxianjiuguo, by pressure and heat so that the liquid to break through the critical point, so that the liquid becomes a (no difference before the liquid and gas) supercritical fluids, intermolecular there is no longer mutual attraction. So Samuel sodium silicate as a starting material selected children, catalytic hydrochloric acid to promote the hydrolysis, water and ethanol as a solvent to convert it into an alcohol gel switch. Then the gel was put in an alcohol environment of high temperature and pressure, until the alcohol which becomes a supercritical fluid, while continuing to maintain the critical temperature, while pressure on the gel, as the pressure is reduced, the ethanol molecules released as a gas out . Then the gel was removed from the heat source, until the cooling liquid of ethanol originally in the gel are volatilized into a gas, leaving a solid structure and which is filled with gas, which is the birth of an airgel. In 1931, research published in \”Nature\” magazine.
Improved methods for the preparation of airgel
There is no doubt that this is a landmark study, but the strange thing is that after 30 years in the airgel research work is almost a standstill, mainly because it was conditions of preparation more difficult, time consuming particularly long. Until 1970, the University of Lyon in order to seek a porous material can be stored oxygen and rocket fuel, pulls out 30 years ago, airgel, and improves the preparation method on the basis of the Samuel children. The new production method using alkoxysilane (of TMOS) instead of sodium silicate, using formaldehyde in place of ethanol, the gel thus produced alcohol out of the gel produced silica aerogels can be of higher quality, additional time also a lot faster, this method is a direct result of a major advances in airgel science. After A method for improving the more the more researchers added to the airgel art. 1983, Berkeley Lab group microstructure materials found TMOS toxic compounds may be replaced by safer tetraethyl orthosilicate (TEOS). And by the sol – gel method to make TEOS hydrolysis and polycondensation. In addition, the microstructure of materials team also found that in supercriticalBefore drying, the gel with the alcohol may be replaced by liquid carbon dioxide, without damaging the aerogels. This liquid carbon dioxide represents a major advance security, because unlike alcohol as carbon dioxide has a risk of explosion.
Other applications of aerogels
With further study airgel, nanoscale particle physicists realized that this material can be used to collect elusive Cerenkov radiation particles, because these particles broke into the airgel structure complicated, it is difficult out through the other end, so as to leave in the airgel. In addition to collecting particles, advancing silica airgel prepared by the NASA Jet laboratory, but also to catch up to the space \”flight\” and was tasked to collect comet particles. Having said that, I believe we all understand the various features and continuous improvement of airgel preparation, no matter from which point of view, it is very good, why has not it spread to public life? First or production, even after preparation of a number of improvements, the most critical or supercritical conditions set threshold. Secondly, airgel industrial production as well as a challenge, and that is very brittle airgel, although its load-bearing capacity is very strong, but unfortunately, it\’s very little tension, breaking a little harder it will be able to \”a is divided into two \”, it is generally also need to add other additives. also have to mention the price, about 6 cubic centimeters airgel price at around 350 yuan, so the cost is also a factor in production and application constraints. But these issues are fundamental, airgel from birth to now, still like a lot of years ahead of future materials with great potential.