Aerogel as an Engineering Material and Its Effectiveness - Case Study Example

Aerogel Name Institution Subject Instructor Date Abstract Aerogel is a manmade solid known to have the lowest density on the planet and has microstructures that are very fine and porous. It is basically made from silicon dioxide that is very amorphous and has grains with sizes between 1.0-10nm which is filled by air forming a 3D structure. Aerogel also has very low conductivities in its various forms therefore possessing enormous insulation capacity. This paper highlights aerogel as an engineering material and its effectiveness in engineering practice. Table of Contents Table of Contents 3 1 Introduction 4 2 Examples and images of materials 4 4 Explanation of the use of the relevant materials 9 5 History of Aerogels 10 7 Environmental impact and sustainability 12 8 Conclusion 13 1 Introduction Aerogel is manufactured from titania, silica, alumina etc and is usually filled with vacuum, water, air or alcohol as stipulated by Aegerter (2011). Additionally, the surface is then modified by the use of carboxyl, amine, and agents for silane coupling, agents for chelating, enzymes and other substances (Mortensen, 2007). Properties of Aero-gel include; Have extremely low density approximately 0.003g/cm3. Has very high porosity ranging from 82% to 99.8% Has very low thermal conductivity. (0.02W/m-k) It has an index of fraction that is extremely low (usually less than 1.05) Its dielectric constant is very low usually k=1.0 to 2.0. Its specific surface area is very high ranging between 500m2 /g and 200m2/g. 2 Examples and images of materials Aerogels are manufactured through the technology of sol-gel and have different types including; cellulose, oxides such as zirkonia and quartz, polymers, starch and basically any material that has gelling qualities. Monolithic Silica Aerogel(Aegerter, 2011) Monolithic silica aerogel (Aegerter, 2011) 2.1 Production of Aerogels Aerogels are formed through two major stages: One process involves the production of the wet gel and the second stage involves the drying of the wet gel resulting to formation of an aerogel by use of Silicon Alcoxide precursors such as tetraethyl orthosilicate as noted by Ashby and Schodek (2009). The use alcoxides are used to improve the various properties of the gel and also for elimination of the appearance of the unneeded by-products of salt. Moreover, it facilitates an increased control of product. Si (OCH2CH3)4 (Lid) + 2H2O Lid =SiO2 (solid) + 4HOCH2CH3 (Lid) The silicon alcoxide concentration used during the process determines the eventual aerogel density and the process are carried out in ethanol. The use of catalysts is essential in the formation of aerogel because at room temperature the reaction is very slow and takes many days or even weeks before the process is completed. The properties of the eventual aerogel product and its physical and microstructure characteristics are determined by the nature and amount of catalyst applied (Mortensen, 2007). Ammonia is used as a basic catalyst while catalysts that are acidic include hydrochloric and portico acid. Gels prepared in a single process involves base or acid catalyzed TEOs. Whether Aerogels are two stage or single stage, the varying formation conditions result to critical modifications to the aerogel product. Nonetheless, two-stage process is preferred to one stage. 2.1.1 Soaking and Aging The condensation and hydrolysis effect of Si (OCH2CH3)4 reactions is deemed complete when the gel point is attained by the sol but this is not the truth. To facilitate silica system strength, enough gelation time need to be provided (Mortensen, 2007). The process should be gradual and should be advanced by managing the content of water and PH of the coating fluid. For gels catalyzed by the base aging procedure, it involves soaking gel in water or alcohol for two days. Thereafter, drying of the gel takes place preceded by the aging of the gel. This is obtained through soaking of the gel in alcohol to such a time when all water disappears. 2.1.2 Drying through super-critical process. This is most essential and the last process of formation of silica Aerogels and involves eliminating the liquid contained in the gel enabling the silica system to have an appropriate linkage (Ashby and Schodek, 2009). This is achieved by earlier replacement of ethanol with carbon dioxide and then venting it at a supernormal temperature or by expelling ethanol at a very high temperature. It’s imperative that the procedure is performed in an autoclave prepared specifically for this process. The procedure is carried out in the following steps: The first step involves filling the autoclave with ethanol and then setting the alcogels on its inside. The arrangement is subsequently cooled to between 6 and 10 degrees centigrade and pressure is applied at around 800 Psi. Ethanol is expelled from the gels by passing liquid carbon dioxide through the system and this process continues until all ethanol is eliminated. After all ethanol has been removed from the system; heat is supplied to the vessel at a critical temperature of 31 degrees C which makes the pressure to increase steadily. Carbon dioxide is then discharged slowly to retain the carbon dioxide at critical pressure. This process proceeds for a short period and later carbon dioxide is released slowly to ambient pressure. The duration required for this procedure ranges from between 15 hours to 7 days. The Aerogel are now ready the vessel can be opened. Figure 1 Supercritical drying process (Ashby and Schodek, 2009) 3 Case Study: Application of aerogel in building and construction. In the United Kingdom, aerogel is extensively used in apartments especially for insulation of interior walls, floor and exterior walls and also for helping the reduction of emissions of carbon and for lowering the energy use. In addition it is used in gas and oil industry for insulation. The U.K government has initiated a project for insulating the civic houses through the use of an aerogel known as Spacetherm and for energy saving, reducing the noise, resisting water and facilitating faster installing. Spacetherm is composed of lamination of two layers of spaceloft with an approximate 30mm of thickness (Ashby and Schodek, 2009). Fibres are combined with silica aerogel to facilitate reinforcement of the material (Mortensen, 2007). Through this method, installation is made easier and thinner and therefore securing increased space for tiny houses. 3.1 Characteristics of space loft. Spaceloft is a heavy blanket made of highly porous and flexible aerogel used for insulation in residential, industrial and commercial buildings. It’s very hydrophobicite and is easy and fast to install, has high resistance to compression, it has ultra-low thermal conductivity and it’s very flexible (Ashby and Schodek, 2009). Additionally, it has a thickness of between 5mm to 10mm and 200 degrees of temperature. It is hydrophobic and has a width of 450mm and a density of 0.15g/cc. Benefits of spaceloft include: Cost-effectiveness Saving of space in small houses due to its thin nature. Fast and efficient installation Reduction of energy use. Reduction of emissions of carbon. Protection against fire. Offers extreme acoustic properties. Has high compressive strength. It’s environmentally benign. Simple to handle. 4 Explanation of the use of the relevant materials Aerogel has various uses which include: Its used in chemical industries for holding catalysts reactions involving chemicals and gases Applied in cleaning up pollutants in the environment acting as a sponge and therefore soaking up the pollutants. Its used in bomb proof equipments. Materials for thermal insulation in pipelines, residential houses and in motor vehicles. Applied in manufacturing components that are electronic in nature such as detectors, sensors, batteries and capacitors. Applied in space technology Used in production of kinetic energy absorbers. Applied in manufacture of super capacitors. Used in making detectors for subatomic particles. Used in chemical catalysis 5 History of Aerogels Steven Kistler produced the first aerogel in 1931 Stockton. At the time, Steven was proving that a gel and a wet gel had the same shape and size and solid network that is continuous. To achieve this objective, he realized that he needed to maintain the solidity of the component by eliminating water from the wet gel. Nevertheless he encountered difficulties since the gel shrunk to a percentage of its normal size when the wet gel dried on its own and which resulted to extensive gel cracking (Aegerter, 2011). Through this process, Kistler learnt that there was a micro-porous characteristic of the solid gel and there were fairly strong forces of tension exertion on the interface of the vapor and liquid upon the liquid evaporation. He concluded that to facilitate aerogel production, air must replace the liquid and avoid the retreating of the liquid within the gel. The first study of gels by Steven was that of silica gels made by condensing liquid sodium silicate with acid. In spite of this, Kistler was unable to change the liquid in the gels to supercritical fluid. There was a re-dissolution of the silica by the supercritical fluid instead of remainder of silica aerogel. Kistler then made another attempt by using alcohol than water and separating salts from the gel through washing by water. Through formation of supercritical liquid by the change of alcohol there was formation of initial true gels. Aerogels produced by Kistler were extremely porous, transparent and possessed density that was very low alike to the present day silica gels. In the following many years, Kistler made Aerogels from different other materials such as rubber, gelatin, alumina, cellulose, tin oxide, nitrate, tungsten etc through which he used to identify his silica Aerogels. Kistler left the college after a number of years and joined a corporation known as Monsanto which initiated marketing for the aerogel and which was used in toothpastes and cosmetics as an additive. Until the 1960s, there was little development on Aerogels when cheap fumed silica appeared in the market. There was rapid development of Aerogels technology afterwards and more people joined the research. The following are the significant events to its development: Researchers in the field of physics made a discovery in the 1980s that detection and manufacture of the Cherenkov radiation would be accomplished by use of silica Aerogels. This experiment was carried out by manufacture of double detectors that were very large. One was filled with silica gel approximately 1000 litres in Sweden at the Lund college and another with 1700 litres of the gel at Hamburg, Germany. Subsequently, there was an establishment of the first plant for silica gel production in Sweden which was achieved via the TMOs technique in 1983. In the year 1983 it was discovered that a safer and better reagent known as TEOs could be applied by the lab at Berkely and by the group known as Arlon Hunt. In 1984, it was discovered that liquid CO2 could be used in the place of alcohol contained in the gel without causing destruction to the aerogel before undergoing the supercritical drying process. This was achieved by the group known as Micro structured Materials. Consequently, the revelation presented a major shift in the aerogel study especially regarding safety since methanol’s critical point presents a much worse condition than that of carbon dioxide. The explosion of alcohol is much more dangerous than that of CO2. The process was used in manufacture of Silica tiles that were transparent. A global symposium was held in Germany in the city of Wurzburg in 1985 where a number of papers on the research were presented. Other symposiums were held in 1994 the city of California ,USA and before that in France (1988) where more research papers were presented During the 1990s, there was an increase in research in the field aerogel and it’s likely that more developments in its applications and technology will continue. 6 Information on appropriate and inappropriate engineering use Aerogels may be effectively utilized in Spacetherm and for energy saving, reducing the noise, resisting water and facilitating faster installing. This is because Spacetherm is composed of lamination that consists of two layers of the spaceloft that has 30mm thickness. They may be used in conjunction with fibre and silica aerogel so as to facilitate reinforcement of the material. They are also used effectively in architecture for isolating walls and lighting. Additionally, the aero gels may be used in the manufacture of space suits. The limitation that occurs in engineering practice is that, they should not be used when the place is damp. This would lead the aerogel to convert back to a gel. There are also difficulties in ascertaining the exact quantity of aerogel as it is difficult to determine the number of pores. 7 Environmental impact and sustainability Production of silica Aerogels involves a use of materials that are generally environmental friendly and as such it doesn’t cause any harm to the environment. The process of doing away with the Aerogels after use is widely natural and they are usually compressed and converted to smooth powder upon disposal. The powder actually resembles sand upon disintegration. Additionally, Aerogels are not flammable and are non-toxic. The continuous use of Aerogels is highly beneficial in preserving the environment and can replace non-biodegradable plastics in the long run yielding sustainable protection of the environment. 8 Conclusion Aerogels form a significant part in modern engineering materials. It has many favorable properties making it appropriate for many applications. It is also environmentally benign making it suitable for environmental protection. Recent research indicates that the uses of aerogel are rapidly growing and has a big impact in sustainable technological developments. As aerogel studies continue, immense commercialization is imminent. References Aegerter, M. A., 2011. Aerogels Handbook. New York, NY, Springer. Ashby, F and Schodek, S. 2009. Nanomaterials, nanotechnologies and design an introduction for engineers and architects. Amsterdam, Butterworth-Heinemann. Mortensen, A. 2007. Concise encyclopedia of composite materials. Amsterdam: Elsevier. Read More