Essay: Silica aerogels – creation and impact

1. Abstract
High-performance insulation simply begins with silica aerogel. Within this particular study, Aerogels will be used as a lightweight solid that is compared to gel. The liquid property of the gel serves as the gas which keeps the material’s density immensely low. The air that composes 97% of the solid impedes on the convection and conduction within the product, while the other 3% is composed of solid clusters. The properties of the aerogels are what qualifies it to be the world’s lowest density solid and efficacious thermal insulator. These successful developments left to Aerogel Technology.
The anticipated outcome will be an accurate methodical presentation that will be able to show how the hot and cold thermal insulation will move farther, further and stronger while being upper-level insulators.
The result of this research paper will be to provide in-depth background on the creation and impacts of aerogels within our nation to show how less dense, how much further, faster and effective the thermal insulator material reacts to other products.
2. Introduction/Background/Literature Review
2.1 Introduction
Silica aerogels were first discovered by Professor Samuel Kistler who was a known educator and also very active in the research field. He has authored many scientific articles and technical books within his years of teaching at the University of Utah. Before retiring Dr. Kistler self-published his nonscientific Memorabilia in the University of Utah Library, which include his life story pertaining to his research and teaching history at the university. Dr. Kistler always had an interest in supercritical fluids. He completed his master thesis at Stanford in 1922, which advocated the crystallization of amino acids from supercritical fluids. The lack of publications of research makes it hard to distinguish when Kistler’s work on aerogels was actually done but it is noted that Kistler did research with Professor McBain publishing a paper on the first wet gels. Kistler started working on the production of aerogel during his summers at Stanford since they were a better equipped University. Kistler premiered his work on aerogel while teaching at the College of the Pacific in Stockton, California. The first publication on aerogel was issued in Nature year 1931.
The first large scale production unit for silica aerogel operations plant is located in Monsanto Chemical Company in Boston, Massachusetts. The first product is a light solid that contains more than 95% air volume. “Silica aerogels are highly porous 3D nanostructures and have exhibited excellent physio-chemical properties. The silica aerogel has a low thermal conductivity, high surface area, and good chemical stability,” says Simulation and Analysis of Mechanical Properties of Silica Aerogels: From Rationalization to Prediction.
2.2 Design Process
Silica aerogels have a density of 1.8 pounds per cubic foot. Silica aerogels consist of a solution of sodium silicate to sulphuric acid. According to Monsanto aerogel plant appeared in Chemical and Metallurgical Engineering February 1943 p.144, “Concentrations are controlled to yield a gel having 8 percent silica. After aging several hours to allow the gel to strengthen, due to syneresis phenomena, it is removed from the tank and passed through the roll crusher into one of four wash tanks. Water is passed up through this tank over the gel to remove the sodium sulfate formed in the gel preparation reaction. When the gel has been sufficiently washed, all excess water is removed by draining and the gel is then covered with alcohol. After suitable soaking time, the alcohol is drained off and replaced with a fresh portion. The alcohol washing procedure is done by the use of a conventional 4-stage counter-current system. Greater economy of alcohol is realized by using the cover, soak and drain method of washing in place of continuous how through the tanks. The counter-current cycle is facilitated by use of the wash receivers and the transfer pump. Weak alcohol taken from the system is recovered as strong alcohol by fractionation in a recovery column.
When the water in the gel has been substantially replaced with alcohol, the excess alcohol is drained off and the gel charged to the autoclave. Here it is heated to 550 deg. F., the pressure being held to 1150 lb. gage by bleeding of alcohol vapor through the condenser. When 550 deg. F. is reached the pressure is reduced to atmospheric and the autoclave is finally evacuated to 20 in. mercury for 10 min. The resultant aerogel is then removed by a conveyor system. The autoclave is heated by a jacket containing diphenyl vapor at 80 lb. gage pressure, this vapor is supplied by the oil-fired diphenyl boiler.
The process is built around one essential unit operation involving a unique step, i.e., the heating of a gel system to temperatures and pressures above the critical for the liquid phase present in the gel,” which is a description of the process used to develop silica aerogels.
Figure 1: The final product of Silica Aerogels which is 3-5 pounds per cubic foot.
3. Material Design Selection
3.1 Criteria
The physical composition of silica aerogels depends on the density and the chemical properties based on the various methods that are used to determine the different properties and composition. Silica aerogels are perfect thermal insulators because of the size of the pores and they are also poor conductors. Silica aerogels can be combined to produce more complex forms such as monoliths, grains, powders, and films which makes the material more flexible depending on the utilization needed. According to Hindwai “NASA has previously used monolithic silica aerogels for the thermal insulation for space applications.” There are three heat transfer mechanisms for silica aerogels which are solid conduction, gaseous conduction processed by gas molecules, and radiation which is when the energy travels in waves through that specific material. The thermal conductivity within silica aerogel is low because the transfer for the heat to pass through has meshed into a network with a standoff resulting in no convection.
3.2 Stress and Strain of Silica Aerogel
Figure 2 and 3 symbolizes the stress-strain curve of the silica aerogel with a relative density of .098 under compressive deformation conditions and the stress for the aerogel structure when it is under 0.1 compression of deformation. The graph shows the three different stages depending on how compressed the material is during that stage. The three images related to the tensile strain with a percentage listed above each image. All of the images represent the compression strain’s different stages which are less than 0.1 (image one), between 0.1 and 0.5 (image two) and over 0.5 (image three). The decimals presented on the graph, Figure 2, correlate to the percentage of tensile strain that shows the linear elastic, plastic yielding and densification of the silica aerogel. Silica aerogels are the lightest solid but are also fragile and brittle due to the composition which makes the material not suitable for heavy loads. According to Hindwai, “Standard methods to characterize the silica aerogel mechanically include ultrasonic techniques, three-point bending, and uniaxial compression.”
Figure 2: Stress-Strain Curve of Silica Aerogel with a relative density of .098 under compressive deformation conditions.
Figure 3: The Von Mises stress for the aerogel structure under 0.1 uniaxial compressive deformations. Structural views for the 5 x 5 x 5, A represents its translucent perspectives and b) represents under 0.1 compressive deformations along the z-axis. The color map shows the Von Mises strain.
4. Aerogels in Aerospace
4.1 NASA Rovers
Silica aerogels are a great insulator because the small pores block the air from circulating. The aerogels were used as an insulation factor on the Sojourner Rover, which is NASA’s flight for mobile vehicle technologies with a mission to determine the performance of a micro-rover on the planet Mars. The Mars rovers Spirit and Opportunity used the silica aerogels to modulate the temperature of the electronics on the rover. Depending on the generation of the silica aerogels they can be used in many different ways. The first generation of aerogels was made very fragile which makes the silica break very easily.
4.2 New Generation of Silica Aerogels
NASA scientist was the first to reveal the new generation of aerogels to the public during a conference. The new generation of aerogels are still thin and flexible but they are also 500 times stronger than the first generation of silica aerogels which results in more insulation than fiberglass. The scientist is still doing research to improve the material. The Glenn Team has started a project called the Hypersonic Inflatable Aerodynamic Decelerator. The project is an “inflatable reentry vehicle that is folded and stowed inside a launch vehicle, “according to NASA. The project allows large mass products to be transported through the atmosphere more securely than previous vehicles, and it also lowers the temperature to keep the vehicle from overheating. The HIAD is sealed with a flexible thermal protection system that uses silica aerogels are the insulator. “The project would like an aerogel that is more flexible, more foldable and doesn’t dust, doesn’t shed insulation particles, so it is not a hazard or messy to handle. In response to that, we started looking at different kinds of polymers and techniques that could make that sort of aerogel more flexible,” Meador says. In the near future scientist predict that the material will be used in more applications such as insulation in automobiles for entry, landing, and descent on different planets. The new generation of aerogels will be used as inflatable insulation that can be stored within the vehicle at the start and then they will be able to distribute into light heat shields.
5 Conclusion/Discussion
5.2 The reasoning for Silica Aerogels Being the Best Material
The material is desirable for the visible properties that it provides to every application. Silica aerogels have an exceedingly low density to create an open nanostructure, low thermal conductivity and are able to absorb fluids very quickly with the sizes of the pores being small. The insulation of silica aerogels cannot be compared to other materials because silica aerogels is a very lightweight but flexible material. The scientist will be able to use the material on many space crafts now and in the future due to how dense the material is. Silica aerogels are great for transportation because of how easy the material is to be packed away and released when needed.
5.3 Next Step
Currently, scientists are researching how to improve silica aerogels. The material is expensive but the new generation of aerogels will be cheaper, more durable and not as hazardous as the previous material. Professor Nicholas Leventis astonished the engineering community in 2002 by making an unbreakable version of silica aerogels. The silica aerogels he invented are called x-aerogels which are stronger, more flexible, water resistant and more durable but the new material is still hazardous due to the chemicals used to produce the material. Scientists are currently trying to apply silica aerogels to use as hydrogen storage media. Metal aerogels are the next generation of aerogels to be produced. Semiconductor aerogels will change the future of energy and fuel, which will help make more smart materials to affect our lives for the better.
2019-3-6-1551902203