Aerogel was found by Steven Kistler in 1931, but its application cannot be in the market and consumer because there is no item that can use the aerogel. The 1980s the aerogel have a place to be a raw material in existing and new product after they discover a new research about aerogel. They have been considered as a new development material that better than polyurethane foam in refrigerators, and as a heat insulator for windows. Aerogel is produced by removing all the water from a colloidal silica gel without collapse its overall structure.
When gels get dry normal temperatures and pressures its affect the surface tension in tiny pores of the gel causes the structure to collapse and reduce itself to roughly 10 times its original volume. To produce aerogel, a gel is placed in a vessel of high heat (280°C or 536°F) and pressure (1800 pounds per square inch, or 1241 Newton’s per square centimeter). This causes all the liquid within the gel to transform into a supercritical state, allowing a phase transition from liquid to gas without the absence of shrinkage which causes a gel structure to collapse and fully dry. This process is known as supercritical drying process.
Before they discover the process, it took days to create aerogels, but improvements have short the drying time to a few hours. The process still needs a high energy, leading to the high cost of aerogels. Aerogels also known as a space age material which is in one day it can be used in a many ways of applications and in material from insulation for housing to new forms of artwork. Many young researchers are make a research on focusing the aerogel, mixing aerogel with filler such as carbon to increase its insulating properties, or working to reduce pore size to make aerogel as transparent as possible.
There are many ways for future research and many potential applications if this research successful. Silica Gel Silica gel is a mixed substance made from silicon silicate that is well known for its ability to absorb and hold in moisture in its substances. Even the term silica gel is used to describe this type of silica substance; it is actually a solid material rather than a gel. This silica is prepare into tiny beads or powder and is often used to absorb in moisture from food products or items where excess moisture would be effect to the quality of the product.
Many consumers find that small packets of this silica and-like substance inside leather products, pepperoni, and mostly electronics. Some of the companies also put packets of the gel inside vitamins to prevent outside moisture from forming inside the capsules or pills. The maximum amount of moisture content in that silica gel can absorb is roughly 40 percent of its total weight. Many people probably guess that once silica gel has absorbed the maximum amount of liquid moisture, it would be useless.
Silica gel can actually be reused for multiple times. To reuse this silica gel, it needs to be heated to approximately 300 degrees F (150 C). Reheating the gel to this high temperature, it will dries up the moisture that has been absorbed, so that it can be reused again. Some people use silica gel for the purpose of drying out flowers in a room. This method is often about time-consuming, but many people prefer it more than other types of flower preservation methods because the results tend to be better when silica gel is used.
There is a type of silica specifically used for drying out flowers called silica sand. People normally place their flowers inside a non-air container along with the silica sand for a short length of time. Silica sand removes away moisture from inside flowers to keep them from drooping and losing their color for short time interval. Contrary to popular belief that silica gel is a toxic, silica gel is not a toxic. Many people are concluding that the gel is toxic because the packets that contain it often have labels on packaging that say, “Do not eat. Even though gel made from silica cannot be considered as a toxic, people should avoid eating it because it could cause some digestive and respiratory upset and it’s not a food for kids to alert. The gel also can become toxic depending on what it has absorbed. For example, the silica was placed inside of a box or bottle that contains some type of poisonous liquid or moisture or a prescription medication that wasn’t suitable for everyone because eating the gel could be life-threatening because it might contain trace amounts of the poison or medicine.
Supercritical Drying When a substance that hold a liquid is dried via normal methods of applying heat and pressure at a certain rate, the substance passes through the liquid-gas border, where the amount of capillary stress changes, that can cause the substance to deflate. This drying process would affect the overall surface tension of the substance, causing the structures to break or change. To prevent this problem, there is supercritical drying, which is dries a substance in via high heat and pressure, and goes around the liquid-gas boundary without moving through it.
The density of the liquid and gas are same and, molecularly, there is no difference between them. Supercritical drying also can be used with supercritical fluids which is there are several different drying methods. The normal drying process involves by using medium heat or pressure and is fine when applied to substances such as water, which are not easily broken. Some substances or devices such as microelectromechanical devices that have tiny machinery will experience an imbalance phenomenon during this drying process because, when the surface tension of the liquid changes to a gas, it pulls and changes against the structure of the substance.
In delicate structures, these changes can create problems. To prevent this surface-tension issue, supercritical drying is one method that skips the liquid-gas boundary and does not affect the substance’s capillary stress. Capillary stress is the space between the substance’s pores and, when the liquid becomes a gas, the capillary stress causes the substance to collapse. So, a supercritical fluid is required to overcome this. These fluids look like liquids but they are able to expand and compress like gases and they also are able to dissolve other substances.
Preparing these fluids need to involves saturating the pores with an organic solvent. There are several ways to performed supercritical drying. In the high-pressure and high-temperature method, a pressure container is filled with the supercritical fluid and the organic solvent which is the supercritical fluid was immersed. The substance is then quickly exposed to heat and pressure that through beyond its critical limit, causing the fluid to change into a gas where capillary stress is maintained.
While the high-pressure and high-temperature method is the simplest way of performing supercritical drying, there is a low-temperature method which is safer, because the other can be explosive, and some substances cannot stand the high pressure and heat. Others than an organic solvent, carbon dioxide is used, because it is supercritical broke at a low temperature. Supercritical drying with this ways is not always successful, because some fluids that mixed and will react with the carbon dioxide to create metal carbonates. Supercritical Fluid
A supercritical fluid is a substance in liquid form that has been heated above its critical point. The critical point of a substance is the point where the critical pressure and temperature exist, they allowing the substance to exist in its liquid and gaseous forms at equilibrium state. The result of taking a substance beyond this point is unique because the fluid has the dissolving properties of a liquid, but the diffusing properties of a gas. That means that it can be dissolve in substances like a liquid while expanding to fill a container like a gas.
These unique properties make it allowed to be used in different industries. When a substance is reach above its critical point, it becomes a supercritical fluid form. In order for a fluid to become supercritical form, the information about a critical temperature and the critical pressure must be known. Normally, a gas at high temperature can be change into a liquid with the present of pressure, and a liquid at high pressure can turn into a gas with the present of heat. The critical pressure is the pressure above which a substance cannot exist as a gas despite how high the temperature is.
Similarly, the critical temperature is the point above which a substance cannot be a liquid despite how high the pressure is. When a substance is heated above the critical temperature and is put under a pressure above that of the critical pressure, an interesting phenomenon occurs. The substance cannot be either a liquid or a gas. Rather, it has the properties of both. The lines between the phases of matter virtually disappear, and the fluid changes properties. The new supercritical fluid has properties of both a liquid and a gas.
One supercritical fluid that is often used is carbon dioxide. It is a good substance to turn into a supercritical fluid because its critical temperature is 87. 8°F (31°C) and its critical pressure is 73 atmospheres (about 55,480 mm Hg). Once it is a supercritical fluid, the properties of carbon dioxide can be altered with changes in temperature and pressure. For example, manipulating the pressure can change which substances will dissolve in the fluid. Since carbon dioxide is a non-polar molecule, modifiers can be added to increase its ability to dissolve polar molecules.
Some supercritical fluids can be used to extract a greater amount of a desired substance in a shorter period of time. These and other properties allow them to be used in a vast array of industries. The food and pharmaceutical industry, for example, can use the fluid to extract certain compounds from food. Using a supercritical fluid, such as carbon dioxide, a scientist can extract fatty acids, oils, and antioxidants without leaving a chemical residue on the extract. Supercritical carbon dioxide also has a relatively low temperature so it can be used in instances where a chemical cannot be exposed to high heat.
University/College: University of Chicago
Type of paper: Thesis/Dissertation Chapter
Date: 13 October 2016
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