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De-icing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only de-ice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prevent adhesion of ice to make mechanical removal easier.
De-icing can be accomplished by mechanical methods (scraping, pushing); through the application of heat; by use of dry or liquid chemicals designed to lower the freezing point of water (various salts or , alcohols, ); or by a combination of these different techniques.
De-icing of roads has traditionally been done with Road salt, spread by or 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 still freezes at , it is of no help when the temperature falls below this point. It also has a tendency to cause corrosion, 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, 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 , 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. Other organic compounds are wood ash and a de-icing salt called calcium magnesium acetate made from roadside grass or even kitchen waste. 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 () as well as at lower overall rates of spreading per unit area.
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 . 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 and the method is still under development.
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.
Ground de-icing methods include:
Ice protection systems typically use one or more of the following approaches:
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.
Ethylene glycol and propylene glycol exert high levels of biochemical oxygen demand (BOD) during degradation in surface waters. This process can adversely affect aquatic life by consuming oxygen needed by aquatic organisms for survival. Large quantities of dissolved oxygen (DO) in the water column are consumed when microbial populations decompose propylene glycol.
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