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Deicing
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== Application areas == === Roadways === In 2013, an estimated 14 million tons of salt were used for de-icing roads in North America.<ref name=Salin>{{cite journal|title=Salinisation of Rivers: An Urgent Ecological Issue|author=Miguel Cañedo-Argüelles, Ben J. Kefford, Christophe Piscart, Narcís Prata, Ralf B.Schäferd, Claus-Jürgen Schulze|journal=Environmental Pollution|volume=173|year=2013|pages=157–67| doi=10.1016/j.envpol.2012.10.011|pmid=23202646|bibcode=2013EPoll.173..157C }}</ref> De-icing of roads has traditionally been done with [[Road salt|salt]], spread by [[snowplow]]s or [[dump truck]]s designed to spread it, often mixed with [[sand]] and [[gravel]], on slick roads. [[Sodium chloride]] (rock salt) is normally used, as it is inexpensive and readily available in large quantities. However, since [[Brine|salt water]] still freezes at {{convert|-18|°C|°F}}, it is of no help when the temperature falls below this point. It also has a tendency to cause [[corrosion]], [[rust]]ing the [[steel]] used in most vehicles and the [[rebar]] in concrete bridges. Depending on the concentration, it can be toxic to some plants and animals,<ref>{{Cite book |first=Marion |last=Fischel |url=http://worldcat.org/oclc/173668609 |title=Evaluation of selected de-icers based on a review of the literature |date=2001 |publisher=Colorado Dept. of Transportation |oclc=173668609}}</ref> and some urban areas have moved away from it as a result. More recent snowmelters use other salts, such as [[calcium chloride]] and [[magnesium chloride]], which not only depress the freezing point of water to a much lower temperature, but also produce an [[exothermic reaction]]. They are somewhat safer for [[sidewalk]]s, but excess should still be removed. More recently, organic compounds have been developed that reduce the environmental issues connected with salts and have longer residual effects when spread on roadways, usually in conjunction with salt brines or solids. These compounds are often generated as byproducts of agricultural operations such as [[sugar beet]] refining or the [[distillation]] process that produces [[ethanol]].<ref>{{cite news |url=https://www.npr.org/templates/story/story.php?storyId=19333950 |publisher=[[National Public Radio]] |title=Beets Part of New Recipe to Treat Icy Roads |author=Amanda Rabinowitz |date=February 25, 2008}}</ref><ref>{{cite news |url=https://www.thestar.com/news/canada/2012/01/21/beet_juice_melts_ice_from_winter_roads.html |title=Beet juice melts ice from winter roads |author=Richard J. Brennan |newspaper=[[Toronto Star]] |date=January 21, 2012}}</ref> Other organic compounds are [[wood ash]] and a de-icing salt called [[calcium magnesium acetate]] made from roadside grass or even kitchen waste.<ref>{{Cite web|url=http://www.theguardian.com/sustainable-business/alternatives-salt-battling-ice-cheese-beets-ash|title=The alternatives to salt for battling ice: cheese, beets and ash|first=Rachael|last=Post|date=March 3, 2014|website=The Guardian}}</ref> Additionally, mixing common rock salt with some of the organic compounds and magnesium chloride results in spreadable materials that are both effective to much colder temperatures ({{convert|-34|°C|°F}}) as well as at lower overall rates of spreading per unit area.<ref>{{cite web |url=http://www.magicsalt.info/Magic%20Salt.htm |title=About Magic Salt |author=<!--Staff writer(s); no by-line.--> |date=2007 |archive-url=https://web.archive.org/web/20090605032512/http://www.magicsalt.info/Magic%20Salt.htm |archive-date=2009-06-05 }}</ref> Several of these new compounds release very small amounts of gases into the air, which are known to be able to cause irritation of the throat and the respiratory tract in humans and animals. The majority of the human population do not experience problems although long-term effects have not been studied. People with sensitive airways, especially infants, may experience serious respiratory problems. Broader scientific studies of the respiratory health problems specifically for people with sensitive airways are lacking (in general, scientific studies have focused on non-respiratory health issues and environmental issues). Solar road systems have been used to maintain the surface of roads above the freezing point of water. An array of pipes embedded in the road surface is used to collect solar energy in summer, transfer the heat to thermal banks and return the heat to the road in winter to maintain the surface above {{convert|0|°C}}.<ref>{{cite web | url = http://www.icax.co.uk/Solar_Runways.html | title = Thermal Energy Storage in ThermalBanks for under runway heating | access-date = 2011-11-24 | publisher = ICAX Ltd, London }}</ref> This automated form of renewable energy collection, storage and delivery avoids the environmental issues of using chemical contaminants. It was suggested in 2012 that [[superhydrophobic]] surfaces capable of repelling water can also be used to prevent ice accumulation leading to [[icephobicity]]. However, not every superhydrophobic surface is icephobic<ref name="NosHej" >{{cite journal| title = Why superhydrophobic surfaces are not always icephobic| journal= ACS Nano| volume=6|issue = 10|pages=8488–8913|doi=10.1021/nn302138r |author1=Nosonovsky, M. |author2=Hejazi, V. | year = 2012| pmid=23009385}}</ref> and the method is still under development.<ref name="Hejazi" >{{cite journal| title = From superhydrophobicity to icephobicity: forces and interaction analysis| journal= Scientific Reports| volume=3|page=2194|doi=10.1038/srep02194 |author1=Hejazi, V. |author2=Sobolev, K. |author3=Nosonovsky, M. I. | year = 2013| pmid=23846773| pmc=3709168|bibcode=2013NatSR...3.2194H}}</ref> === Trains and rail switches === [[File:Icy train brake.jpg|thumb|300px|Ice build up in train brakes jeopardizes effective braking.]] Trains and [[rail switch]]es in Arctic regions can have significant problems with snow and ice build up. They need a constant heat source on cold days to ensure functionality. On trains it is primarily the [[brakes]], [[suspension (vehicle)|suspension]], and [[Railway coupler|coupler]]s that require heaters for de-icing. On the rails it is primarily track switches that are sensitive to ice. High-powered electrical heaters prevent ice formation and rapidly melt any ice that forms. The heaters are preferably made of PTC material, for example [[PTC rubber]], to avoid overheating and potentially destroying the heaters. These heaters are self-limiting and require no regulating electronics; they cannot overheat and require no overheat protection.<ref>{{cite report |title=2012 Autumn & Winter season |date=September 2012 |series=Drivers' briefing |place=London, UK |publisher=First Capital Connect }}</ref> === Aviation === [[File:A U.S. Army C-37B aircraft transporting Army Chief of Staff Gen. Raymond T. Odierno, gets de-iced before it departs Joint Base Elmendorf-Richardson, Alaska.jpg|thumb|300px|A U.S. [[C-37B]] VIP jet gets de-iced before departing Alaska in January 2012]] {{main|Icing (aviation)}} ==== Ground de-icing of aircraft ==== {{main|Ground deicing of aircraft}} On the ground, when there are freezing conditions and [[precipitation (meteorology)|precipitation]], de-icing an aircraft is commonly practiced. Frozen contaminants interfere with the aerodynamic properties of the vehicle. Furthermore, dislodged ice can damage the engines. Ground de-icing methods include: * Spraying on various [[aircraft deicing fluid]]s to melt ice and prevent reformation * Using unheated forced air to blow off loose snow and ice * Using infrared heating to melt snow, ice, and frost without using chemicals * Mechanical deicing using tools such as brooms, scrapers, and ropes * Placing an aircraft in a warm hangar ==== In-flight de-icing ==== {{main|Ice protection system}} Ice can build up on aircraft in flight due to atmospheric conditions, causing potential degradation of flight performance. Large commercial aircraft almost always have in-flight ice protections systems to shed ice buildup and prevent reformation. Ice protection systems are becoming increasingly common in smaller general aviation aircraft as well. Ice protection systems typically use one or more of the following approaches: * pneumatic rubber "boots" on leading edges of wings and control surfaces, which expand to break off accumulated ice * electrically heated strips on critical surfaces to prevent ice formation and melt accumulated ice * bleed air systems which take heated air from the engines and duct them to locations where ice can accumulate * fluid systems which "weep" de-icing fluid over wings and control surfaces via tiny holes ==== Airport pavement ==== De-icing operations for airport pavement ([[runway]]s, [[taxiway]]s, [[Airport apron|aprons]], [[taxiway bridge]]s) may involve several types of liquid and solid chemical products, including [[propylene glycol]], [[ethylene glycol]] and other organic compounds. Chloride-based compounds (e.g. [[salt]]) are not used at airports, due to their corrosive effect on aircraft and other equipment.<ref name="EPA airport-TDD">{{Cite report |date=April 2012 |title=Technical Development Document for the Final Effluent Limitations Guidelines and New Source Performance Standards for the Airport Deicing Category |url=https://www.epa.gov/eg/airport-deicing-effluent-guidelines-documents |publisher=U.S. Environmental Protection Agency (EPA) |location=Washington, D.C. |id=EPA-821-R-12-005}}</ref>{{rp|34–35}} [[Urea]] mixtures have also been used for pavement de-icing, due to their low cost. However, urea is a significant pollutant in waterways and wildlife, as it degrades to [[ammonia]] after application, and it has largely been phased out at U.S. airports. In 2012 the [[U.S. Environmental Protection Agency]] (EPA) prohibited use of urea-based de-icers at most commercial airports.<ref>{{cite web |url=https://www.epa.gov/eg/airport-deicing-effluent-guidelines |title=Airport Deicing Effluent Guidelines |author=<!--Staff writer(s); no by-line.--> |date=2021-02-10 |publisher=EPA}}</ref> ===Water agitator de-icer=== {{See also|Ice jacking|Properties of water#Density of water and ice}} Water agitators are electric motors put under water that propel up warmer water and [[Agitator (device)|agitate]] the surface with it to de-ice aquatic structures on rivers and lakes in freezing temperatures. There are also agitator bubblers that use [[compressed air]], run through a [[Air line|hose]], and released to agitate the water.<ref>{{cite web | url=https://www.splashymcfun.com/blogs/news/what-to-look-for-when-buying-a-dock-de-icer | title=What to Look for when Buying a Dock De-Icer }}</ref>
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