The method of preparing silica airgel in the research and development process and
Many people think that theis the latest product of technology. In fact, in 1931, scientists made the first airgel. At that time, California Stockton, California Institute of Peace Steven Koestler first to prove \”gel\” is included in the continuous web-like solid wet gel of the same size and shape. And this hypothesis proved most obvious approach is to remove liquid from the wet gel without damage to its solid content. In general, however, this method will encounter significant obstacles, difficult to achieve. If the wet gel can simply be dried, the shrinkage of the gel itself, is usually only a fraction of the original size. And this contraction is usually accompanied by serious cracks. Kessler speculated that the solid component is a microporous gel, liquid evaporation of the liquid – gas interface may have a strong surface tension, filled with porous structure. Kessler then found a major factor in the preparation of aerogels: \”Obviously, if one wishes to produce an airgel (Kessler considered creating\” airgel \”), he must with air instead of liquid, wherein the surface of the liquid within the gel contraction is not allowed. If the liquid has been subjected to pressure greater than the pressure of the gas, and the temperature increases, it is converted to a gas at the critical temperature, and any two phases does not exist time. \”(SSKistler, J.Phys.Chem.34,52,1932). the first study Kessler gel was prepared by condensation of an acidic aqueous solution of sodium silicate. But by water into these gels is the supercritical fluid to prepare aerogels have failed attempt to speak. Unlike the last to leave the preparation of , supercritical water may be re-dissolved silica, and then discharged with the water to form a precipitate. At that time it was generally understood that the hydrogel can be exchanged with a water-miscible organic liquid. Kessler thoroughly with water, and then try a clear silica gel (salt solution out of the gel), and then replace the alcohol with water. By alcohol is converted to a supercritical fluid and allowed to overflow, the formation of airgel on the first real sense. Kessler airgel is also very similar to silica aerogels prepared us now. They are transparent, low-density and highly porous materials, which greatly stimulated the interest of the academic community. In the next few years, Kessler silica airgel fully characterized, and many other materials from the airgel, such materials include alumina, tungsten oxide, oxygenIron oxide, tin oxide, nickel-tartaric acid, cellulose, cellulose nitrate, gelatin, agar, egg white and rubber. A few years later, Kessler left the Pacific College and worked at Monsanto, after Monsanto began marketing one kind referred to simply as \”airgel\” products. Monsanto is granular silica airgel materials, processing conditions for the manufacture of such materials are poorly understood, but it is widely believed that production in line with Kessler\’s program. Monsanto airgel is used as an additive in cosmetics and toothpaste or thixotropic agent. Over the next three decades, airgel research little progress. Finally, in the 1960\’s, the development of low-cost silicon dioxide \”pyrolysis\” weakened the airgel market, Monsanto discontinued. In the late 1970s, the French government contacted Clyde Bernard University, Stanislaus Teichner, Lyon seeking a method of storing hydrogen and rocket fuel in the porous material. Among researchers in the field of aerogels pass on the legend of what happened next. Teichner for graduate appointed a task for this application to prepare and study aerogels. However, using the method of Kessler, wherein the solvent exchange step comprises two time-consuming, require their first weeks to prepare aerogels. Kessler then informed his students, they need a lot of airgel samples to complete his dissertation. I realize that this will take many years to complete, his students have a nervous breakdown and left Kessler\’s laboratory. But after a short break, Kessler determined to go find a better synthesis process. This is a direct result of one of the major advances in airgel science, namely sol – gel chemistry applied in the preparation of silica aerogels. The method Kessler method alkoxysilane sodium silicate (sodium silicate plus four, TMOS), TMOS a hydrolysis step can be generated in a methanol solution gel (be \”alcogel\”). This method eliminates the defects Kessler two methods, i.e., the exchange step and the gel water and alcohol in the presence of an inorganic salt. Alcohol under supercritical conditions, these gels can be dried to produce high quality silica airgel. In the years that followed, Teichner team and others have also expanded this approach to the preparation of various metal oxide airgel. After this discovery, as more and more researchers to join the field, new developments in aerogels science and technology have sprung up, some notable achievements as follows: In the early 1980s, particle physicists realized that silica airgel will be the production and Lun Kefu ideal medium for detection of radiation. These experiments require large blocks of radiation transparent silica airgel. Researchers TMOS method for producing the two large detectors. 1700 liters using a silica airgel in Hamburg, Germany Deutsche elevator Synchrotron (DESY) in the TASSO detector, the other using 1000 liters of silica airgel at Lund University in Sweden in CERN. A method for producing a silica airgel monoliths TMOS first pilot plant was established by Lund, Sweden Sjobo group. The apparatus includes a 3000 l autoclave, a supercritical methanol process releases heat and pressure (240 deg.] C and 80 atm). However, in 1984, occurred in the autoclave leak during a production run, the room containing the container filled with methanol vapor quickly, then exploded. Fortunately, this incident is not dead, but the facility was completely destroyed, then rebuilt the plant, and continue to use the TMOS process to produce silica airgel, the plant currently operated by Airglass company. In 1983, Berkeley Lab Arlon Hunt and micro-structural materials group found a very toxic compound TMOS can be a safer agent tetraethylorthosilicate (TEOS) replacement, and will not reduce the production of aerogels quality. At the same time, the group also found that the microstructure material prior to supercritical drying, alcohol within the gel may be liquid carbon dioxide Alternatively, and without prejudice to the airgel itself. This also significantly improves the safety of the preparation of the production, because the critical point of carbon dioxide occurs (31 ℃ and 1050 lbs / square inch) is much higher than the critical point of methanol (240 deg.] C and 1600 lbs / ft) Low conditions. In addition, the carbon dioxide will not cause as much as alcohol explosion hazard. The method for producing a transparent silica airgel tiles TEOS. BASF, Germany with the development of carbon dioxide from the sodium alternative method of preparing silica airgel beads. This material until 1996 formally production, and \”BASOGEL\” sales. In 1985, Jochen Fricke teachGranted in Wurzburg, Germany organized the First International Symposium airgel, the conference presented 25 papers of researchers from around the world, followed by the International Safety Management Agreement in 1988 (Montpellier, France) 1991 (Würzburg) and 1994 (Berkeley, CA, USA) was held. Fourth of ISA agreement a total of 150 people attended, 10 parts of invited papers, 51 papers and 35 poster presentations. The fifth ISA recently held in Montpellier, there are nearly 200 of the participants. The late 1980s, 劳伦斯利佛莫 Seoul National Laboratory (LLNL) researchers Larry Hrubesh dominated the world\’s lowest density silica airgel (also known as the lowest density solid material) was prepared. The airgel density of only 0.003g / cm3, only three times the air. Thereafter, LLKL Rick Pekala also the techniques for preparation of inorganic aerogels extended to the preparation of organic polymer airgel ,, These include resorcinol – formaldehyde, melamine – formaldehyde aerogels, they isophthaloyl phenol – formaldehyde airgel pyrolysis to yield pure carbon airgel, which opened up a whole new field of research airgel. Thermaxlux L.P. in 1989, founded by Arlon Hunt et al. In Richmond, California. Thermalux company runs a 300-liter autoclave, carbon dioxide production Alternatively TEOS silica airgel monolith. Airgel Thermalux lot of preparation, but unfortunately, in 1992, it stopped working. In the painting propulsion laboratory prepared silica airgel, it has been used in multiple space shuttle. In these vehicles, the main use of very low density airgel to collect and bring back samples of dust in the universe of high speed. Researchers at the University of New Mexico C.Jeff Brinker and Doug Smith and researchers from other institutions increasingly successful by chemically modifying the surface of the gel before drying to eliminate supercritical drying technology used in the production of aerogels, which Nanopore term work led to the establishment of the company, and the commercialization of low-cost airgel. In 1992, in Frankfurt, Germany\’s Hoechst company also began producing low-cost granular aerogels. Aerojet in Sacramento, CaliforniaCompanies with Berkeley Lab. LLNL has carried out cooperation projects, and in 1994 carbon dioxide airgel alternative processes for commercialization. Previously obtained from the Aerojet\’s operating Thermalux 300 liter autoclave, and used to produce various forms of silica, resorcinol-formaldehyde, and carbon aerogels. However, this program also in 1996 was abandoned. With the increase of R & D investment, airgel technology and applications in recent years, often far we gained progress and development. Aerogels are currently being accepted by more and more civil, the value of its role increasingly widespread.