This essay is a general look at aerogels that relies a lot on the articles based on the ‘Ernest Orlando Lawrence Berkely Laboraty (EANDELBL) Website.’ (I have also used this website in my research. The index page is located at ) Nonetheless, the article does summarise a lot of the main points about aerogels helpfully and was a good grounding for my reading before I tackled some of the more detailed sources. Some of the descriptions(such as ‘How Aerogels Are Produced’) seem to be a confused abridgement of the articles on the EANDELBL pages, though the sections describing the physical and chemical properties of aerogels and how they absorb kinetic energy were concise and a useful support in the rest of my reading. Furthermore, the author goes on to suggest his/her own opinions on how silica aerogels could be valuable as a protective and insulating material in the future, and suggests how the obstacle of production cost could be overcome. I found that in this passage, the denotion of silica aerogel as a ‘transparent’ substance was confusing, as a lot of my other sources point out how aerogels are currently unable to be used in windows, skylights, etc. as they are not fully transparent.(they display a bluish haze due to Rayleigh scattering. I am not entirely familiar with the concept, though it seems that if a particle is smaller than the wavelength of light then it scatters light less effectively, thus showing transparency. I shall comment on this in my information booklet, when looking at current ways of solving the problems with aerogels, such as their brittleness and lack of complete transparency). Whereas other articles mention the possibility of aerogel windows when complete transparency is achieved in the production stage, the author of this source states that silica aerogel is not transparent at frequencies above the visible spectrum, and that they could “be incorporated into window panes” in the present.
http://eande.lbl.gov/ECS/Aerogels/saoptic.htm
“Optical Properties of Silica Aerogels”
The optical properties of silica aerogels are explained in immense detail in this source. I found that the paragraph on Rayleigh Scattering was very useful in helping me to have an idea of what many of the other articles were conveying when they described attempts at increasing transparency. After the paragraph on Rayleigh Scattering, the article became far too technical for me to understand, and I could not even guess at what the author was trying to explain. On the whole, the source was vital because the small paragraph on Rayleigh Scattering aided my understanding of other sources, though totally incomprehensible to me after that point.
http://eande.lbl.gov/ECS/Aerogels/sapore.htm
“The Pore Structure of Silica Aerogel”
This source comments on the pore structure of silica aerogels and how this is analysed. The portions of the article that illustrated how pore size is determined were of little use to me, but there were other parts of it that were useful, namely the description at the end of the page where the difference between a closed pore network and an open one is explained. This elucidates why the two different types of silica aerogel, hydrophilic and hydrophobic, behave the way they do, something that is mentioned in other sources but not explained. Hence, the article was useful as it disclosed information that was paramount to my understanding of other areas of my research.
http://www.homestead.com/ipmofalaska/files/DE.html
“Diatomaceous Earth and Silica Aerogel”
It is worthy of note that the application of silica aerogels to pest control was one that was not mentioned anywhere else during my research other than in this source. Therefore, it is useful in a sense because of its rarity. The source is basically a bulletin that briefly describes the use of silica aerogel as a “low toxicity pest control.” In other articles, I have found that silica aerogel is noted for its benignity regarding the environment, as when disposed of it crushes into a fine white powder that, in essence, ‘wastes away.’ Moreover, when it is produced with an ‘open’ pore network, it behaves in a similar way to a sponge and is exceptionally effective at absorbing moisture. Although only short, this source describes fully all that is needed to know about the use of silica aerogels in killing insects, and is for that reason very useful.
http://eande.lbl.gov/ECS/Aerogels/saprops.htm
“Physical Properties of Silica Aerogels”
In my information booklet, I use the density and internal surface area of silica aerogel in two calculations that serve to back up a quite extravagant comparison. The table in this source contains the values I have taken for density and surface area, and are similar to tables I have found on both other reference websites and company websites. Though some of the properties are beyond my understanding(Poisson’s ratio, for example), most are not and are useful when comparing, say, the tensile strength of silica aerogel with other materials. The table also verifies that silica aerogel is the lightest known solid, and that the diversity of the production process means that some of the properties of aerogels are spread over a comparatively large range(density varies from 0.003 – 0.35 gcm-3.) Although some of the data in this and other tables on physical properties is different, I believe that this is due to the times at which the properties were measured, as lighter and stronger aerogels are being produced all the time. This is the most useful of the sources I have found on physical properties, as explanations are given at the side of each value, for instance we are told that the density ranges from 0.003 – 0.35 gcm-3, but that the most common density is approximately 0.1gcm-3. E
http://eande.lbl.gov/ECS/Aerogels/saschem.htm
“The Surface Chemistry of Silica Aerogels”
This article explains, in chemical terms, why silica aerogel absorbs water, and why the hydrophilic types turn into a fine white powder when they come into contact with water. As with the article on “How Silica Aerogels Are Made” I was able to grasp the basic ideas of the chemistry of silica aerogels(due to the images supplied in conjuntion with the text), though a lot of the article was beyond my understanding. The source was not too useful on the whole as I have collected other sources that are much easier(for me) to understand.
http://eande.lbl.gov/ECS/Aerogels/sakinegy.htm
“Silica Aerogels for Absorbing Kinetic Energy”
This was a tremendously useful and valuable source in both aiding my understanding and providing data that was helpful to the investigation. The author points out that though silica aerogels are brittle, their low density means that they are, conversely, very good at absorbing kinetic energy. Moreover, the author points out that unlike other protective materials, there is little rebound when an object impacts with silica aerogel, meaning it is far more safe. It is for this reason that silica aerogels have been used in space to capture fast-moving particles in space, as they slowly bring an impacting object to a halt with minimum damage. I was able to constantly refer back to this source as a reference when attempting to comprehend other sources, and the explanations given are clear and to the point.The graphs included with the article were helpful in visualising what happens when an object hits silica aerogel, and the potential uses listed at the end served the purpose of steering my research towards other areas.
http://eande.lbl.gov/ECS/Aerogels/sawork.htm
“How Do You Work With Silica Aerogel Without Breaking It?”
This source was not particularly useful as it is just a few paragraphs that advise people on handling silica aerogel. All I could gain from the source was a reiteration that silica aerogel absorbs moisture well and has a very low toxicity.
http://eande.lbl.gov/ECS/Aerogels/satcond.htm
“Thermal Properties of Silica Aerogels”
I was able to use parts of this article to assist in my understanding of why silica aerogels do not conduct heat well(i.e. why they are good insulators). As a result, this source was useful as the parts that I needed for my investigation(up to “Minimizing the gaseous component of thermal conductivity”) were relevant and explained clearly. Aside from this, the article was of no use as it depicts methods of obtaining the thermal conductivity of silica aerogel and was highly technical. Moreover, I have no knowledge Pressure/Thermal Conductivity Graphs, so these sections did not help me in my investigation.
http://eande.lbl.gov/ECS/Aerogels/sacomp.htm
“Silica Aerogel Nanocomposite Materials”
An overview of different silica aerogel composite materials and how they are produced is given in this article. I could not ascertain much about specific applications of these composites and some of the explanations were too technical. However, I determined the basics of how and why these composites were produced, which led me to investigate other sources. I eventually found another source that described a specific use of one of these composites and how they had been produced in more comprehensible terms. Nonetheless, this source was useful as it led my research to articles that explained how scientists are tackling improvements in silica aerogels at the moment.(See Below)
http://www.solgel.com/articles/Oct02/straerog.asp
“100 Times Stronger Aerogels May Yield Safer Buildings…”
This is a news story that outlines a very recent successful attempt by scientists to improve the strength of silica aerogels. This article was useful as it assumed less knowledge of chemistry than the previous source when describing the method used to produce new silica aerogel composite materials. I have found this source useful when writing my information booklet, as it demonstrates current strategies that scientists are employing to tackle problems with silica aerogels that preclude their widespread use.
http://eande.lbl.gov/ECS/Aerogels/sao2sens.htm
“Optical Oxygen Sensor Based on Silica Aerogel”
This is a fascinating article that describes the use of silica aerogel as an optical oxygen sensor due to the fact that photoluminescence can be induced in composites of the material, which is consequently inversely proportional to the amount of oxygen absorbed by it. However, I have decided to focus on other applications of silica aerogel so this source was not required when producing my information booklet.
http://www.aerogel.com/products.htm
“Products”
This is a the properties page for a specific commercially produced aerogel in the form of a flexible blanket that can be cut, bent, etc; manufactured by the “Aspen Aerogels INC” company. The source is useful as an affirmation of the data listed in the Berkeley Lab source(See “Physical Properties of Aerogels”). Although a different density range is displayed(0.06 – 0.12 gcm-3 instead of 0.03 – 0.35 gcm-3.) this can be explained by the fact that the company manufactures a specific type of silica aerogel.(The Berkeley Lab Table states the full range of recorded values for density, surface area, etc. whereas this source only states the values for the silica aerogel’s it produces.) I have not used this source as a reference when producing my information booklet as it does not contain as much data or explanations as in the Berkeley Lab Table, but it was still useful as it demonstrates what properties silica aerogels that are being commercially manufactured possess and it also confirms the data I had previously researched.
http://www.aerogel.com/technology2.htm
“Technology”
This is similar to the previous source, and is the company’s list of properties for the whole range of silica aerogels that they can produce. It is useful as it confirms the data in previous sources and supplies some helpful explanations about each property. Nonetheless, I have not used it when creating the information booklet as it does not contain as much data as in the “Physical Properties of Silica Aerogels” source which I have already obtained.
http://nctn.hq.nasa.gov/innovation/Innovation55/techemer.htm
“Technologies Emerge From Mars”
Dated October 1997, this article gives information regarding the “Mars Pathfinder” mission, in which a robot was sent into space to explore Mars. There is a lot of material that is irrelevant to my research on silica aerogels, but there is one paragraph that explains how they were used to insulate the Pathfinder robot to “keep its vital electronics at operating temperature.” The paragraph carries on to give a brief description of what silica aerogels are, but the source is mainly useful as it highlights a use of silica aerogel as an insulating material, and points out some possible applications in the future.
http://www.ceramicjournal.org/issues/v83n3/abs/0099.html
“Synthesis and Characterization of Low-Dielectric Silica Aerogel Films”
This article was completely useless, as it is not complete and may as well have been written in another language owing to the limits of my understanding.
http://science.nasa.gov/newhome/headlines/msad26oct98_1.htm
“Right Stuff for the Super Stuff”
This was a very useful article that outlines the first stage in implementing silica aerogel into windows, and the many benefits of doing so. The author explains that aerogels cannot currently be used in windows because of their lack of complete transparency, and describes astronaut how John Glenn(the first American to orbit the globe, in 1962!) will be part of a team that is entering space to manufacture aerogel there. As with every source I have discovered on this intriguing area of silica aerogel production, the reasons why complete transparency cannot be achieved are not clear(unintentional pun). It is known that lack of transparency is due to the appearance of impurities in the aerogel during the production process, though the reason for their appearance cannot be explained(in any sources I have found, anyway). However, it is believed that a space environment will rid silica aerogels of these impurities, and this source is useful for pointing this out. Moreover, the source is helpful as it places silica aerogel in an economic and social context; if completely transparent silica aerogel can be mass-produced at a reasonable price, then the benefits would be huge. “A single one-inch window pane of aerogel is equivalent to the insulation provided by 32 window panes of glass.” Clearly, this would lead to huge savings in energy consumption. (In another source I read(I have unfortunately lost it) the use of silica aerogel as an insulation material in refrigerators is pointed out. In the Clean Air Act of 1990, the U.S. agreed to cut down on CFC emissions by the end of the century by replacing the CFC-propelled refrigerant foams currently in use with a more environmentally friendly and effective insulation material. They were to choose between silica aerogel, silica powder and glass beads. Silica Aerogel is the most effective, but all three would considerably cut CFC emissions, Carbon emissions and reduce energy consumption. It is unclear why, in 2002, they still haven’t done this.)
http://www.mkt-intl.com/aerogels/silica.html
“Silica Aerogels”
This source is from a company that produces silica aerogels; it lists their properties and gives a brief description of what silica aerogels are and what size they are available in for purchase. It is useful as it affirms the data in similar tables I have found in other sources. However, it is not an essential source, as the table of physical properties I use for reference is the one in the Berkeley Lab Source(See “Physical Properties of Silica Aerogels”), as it is slightly clear because of the explanations it lists alongside each value.
http://stardust.jpl.nasa.gov/overview/
“Welcome”
This is an introduction to what the “Stardust” Space Mission is, and when it was conjectured. This is one of the main applications that my information booklet will focus on, and this source was a helpful piece of background information, though not vital to my research.
http://stardust.jpl.nasa.gov/overview/faq.html
“FAQ’s – Frequently Asked Questions and Gee Wiz Facts”
Again, this is useful background information to the Stardust space mission, and contained some interesting facts about it. In addition, there is a lot of facts about aerogels, though they are only short reiterations of topics that other sources have concentrated on in more depth. This source was not essential in my research, but I found it helpful for learning some of the basic information about the Stardust space mission.
http://stardust.jpl.nasa.gov/tech/aerogel.html
“Aerogel”
This was an extremely useful source. In it, the basic properties of silica aerogels are conveyed. More importantly, those properties that relate to the Stardust space mission are emphasised and explained, and used to justify the use of silica aerogels in the project. The images were useful, and all aspects of the Stardust mission that used aerogels were described, in addition to other possible uses.
http://stardust.jpl.nasa.gov/cool.html
“Cool Facts”
This source is rendered useless after reading the latter sources about the Stardust space mission as it is basically a list of facts taken from them that have then been condensed. I found no use for this source.
http://science.nasa.gov/newhome/headlines/msad19jun96_1.htm
“Frozen Smoke”
This is a useful source that links in with the “Right Stuff For the Super Stuff” article above. It is a bulletin that confirms the production of aerogel in space having taken place, and states that “Comparisons of gels manufactured in space and on the ground have shown large differences, and the production of gels in space can provide a higher-quality product with a more uniform structure.” This affirms the information in the “Right Stuff for the Super Stuff” but the article unfortunately does not mention if complete transparency was achieved. From what I have gathered, it seems that, as slight changes in the production process(say a slight dip in temperature) can affect the outcome a lot, scientists are still working towards a perfect production process that removes any impurities, which can affect the transparency of the aerogel. Aside from the information that aerogel has been produced in space, there is no new information here that I haven’t come across before in my research, so the majority of the source isn’t entirely useful.
http://science.nasa.gov/newhome/headlines/msad08oct96_1.htm
“Aerogel Update!!!”
This is a news bulletin in a similar manner to the one above. However, this source is much more useful, as it confirms that gravity does affect silica aerogel production and goes on to explain about how pore sizes have been made more regular in space, and why they affect transparency.(the impurities I mentioned are actually pores that are slightly larger than other pores in the silica aerogel, and hence scatter light; this gives the silica aerogel a bluish haze and impedes complete transparency.)
http://science.nasa.gov/newhome/headlines/msad08jul97_2.htm
“Aerogel – and the Mars Rover”
This source isn’t very useful as it just repeats the information in the latter two sources and includes a brief notice about the use of silica aerogel as an insulating material in the Mars Pathfinder mission.
http://science.nasa.gov/newhome/headlines/msad05mar97_1.htm
“Frozen Smoke”(N.B. This is different to the source above of the same title)
This source was useful as it makes comparisons of aerogel’s properties that make them easy to understand. For example, we are told that a one-inch thick aerogel window has the same insulation value as 15 panes of glass and trapped air. However, this conflicts with the “Right Stuff for the Super Stuff” article, in which a one-inch thick aerogel window is said to equal 30 panes of glass. This can be accounted for by the fact that there is over one-and-a-half years between the times at which each source was published. This serves to demonstrate how quickly aerogel’s properties are being improved! However, the distance between sources worryingly affirms that scientists are still finding it difficult to produce completely transparent aerogel, as both sources comment on the capabilities of such a material. This source also states some of the properties of silica aerogel – this wasn’t particularly useful, as I have already discovered four such tables in my research.
