Deicing fluid
Encyclopedia
Ground deicing
of aircraft is commonly performed in both commercial and general aviation. The fluid used in this operation is called de-icing or deicing fluid. The abbreviation ADF (Aircraft Deicing Fluid) is often used.
(EG) or propylene glycol
(PG), along with other ingredients such as thickening agents, surfactant
s (wetting agents), corrosion inhibitor
s, and colored, UV-sensitive dye. Propylene Glycol
-based fluid is more common due to the fact that it is less toxic than ethylene glycol
.
The Society of Automotive Engineers publishes standards (SAE AMS 1428 & AMS 1424) for four different types of aviation deicing fluids:
Deicing fluids containing thickeners (types II, III, and IV) are also known as anti-icing fluids, because they are used primarily to prevent icing from re-occurring after an initial deicing
with a type I fluid.
or ethylene glycol
. Other ingredients vary depending on the manufacturer, but the exact composition of a particular brand of fluid is generally held as confidential proprietary information.
Based on chemical analysis, the U.S. Environmental Protection Agency has identified five main classes of additives
widely used among manufacturers:
The use of 1,3-propanediol
(a fermentation product of corn) as a base for deicing fluid was patented in 2009. At least one manufacturer of deicing fluids (Kilfrost) is now using that as a base for their product.
The cost of fluid varies widely due to market conditions. The amount deicing service companies charge end users is generally in the range of US$8 to US$12 per diluted gallon.
The total annual usage of deicing fluids in the U.S. is estimated to be approximately 25 million USgals (94,635,300 l), broken down as follows (figures from 2008, adjusted to show totals for undiluted fluid):
The FAA publishes official Holdover Time Tables for all approved deicing fluids, and revises them annually.
Deicing fluids work best when they are diluted with water. For example, undiluted Dow UCAR Deicing Fluid(type I ethylene glycol), has a freezing point of −28 °C. Water, of course, freezes at 0 °C. However, a mixture of 70% deicing fluid and 30% water freezes below −55 °C. This is known as the eutectic concentration, where the freezing point of the mixture is at its lowest point, and lower than either of the component substances.
Depending on the manufacturer, deicing fluids may be sold in concentrated or pre-diluted formulations. Dilution, where necessary, must be done according to ambient weather condition and the manufacturer's instructions in order to minimize costs while maintaining safety.
The dilution of a particular sample of fluid (and hence its freezing point) can be easily confirmed by measuring its refractive index with a refractometer
, and looking up the result in the deicing fluid manufacturer's tables.
Deicing
For snow and ice control on roadways and similar facilities, see Snow removalDe-icing is defined as removal of snow, ice or frost from a surface...
of aircraft is commonly performed in both commercial and general aviation. The fluid used in this operation is called de-icing or deicing fluid. The abbreviation ADF (Aircraft Deicing Fluid) is often used.
Types
Deicing fluids come in a variety of types, and are typically composed of ethylene glycolEthylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
(EG) or propylene glycol
Propylene glycol
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...
(PG), along with other ingredients such as thickening agents, surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
s (wetting agents), corrosion inhibitor
Corrosion inhibitor
A corrosion inhibitor is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy. The effectiveness of a corrosion inhibitor depends on fluid composition, quantity of water, and flow regime...
s, and colored, UV-sensitive dye. Propylene Glycol
Propylene glycol
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...
-based fluid is more common due to the fact that it is less toxic than ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
.
The Society of Automotive Engineers publishes standards (SAE AMS 1428 & AMS 1424) for four different types of aviation deicing fluids:
- Type I fluids have a low viscosityViscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
, and are considered "unthickened". They provide only short term protection because they quickly flow off surfaces after use. They are typically sprayed on hot (130–180°F, 55-80°C) at high pressure to remove snow, ice, and frost. Usually they are dyed orange to aid in identification and application. - Type II fluids are "pseudoplastic", which means they contain a polymerPolymerA polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic thickening agent to prevent their immediate flow off aircraft surfaces. Typically the fluid film will remain in place until the aircraft attains 100 knots or so (almost 200 km/h), at which point the viscosity breaks down due to shear stressShear stressA shear stress, denoted \tau\, , is defined as the component of stress coplanar with a material cross section. Shear stress arises from the force vector component parallel to the cross section...
. The high speeds required for viscosity breakdown means that this type of fluid is useful only for larger aircraft. The use of type II fluids is diminishing in favour of type IV. Type II fluids are generally light yellow in color. - Type III fluids can be thought of as a compromise between type I and type II fluids. They are intended for use on slower aircraft, with a rotation speed of less than 100 knots. Type III fluids are gaining acceptance in the regional and business aviation markets. Type III fluids are generally light yellow in color.
- Type IV fluids meet the same AMS standards as type II fluids, but they provide a longer holdover time. They are typically dyed green to aid in the application of a consistent layer of fluid.
Deicing fluids containing thickeners (types II, III, and IV) are also known as anti-icing fluids, because they are used primarily to prevent icing from re-occurring after an initial deicing
Deicing
For snow and ice control on roadways and similar facilities, see Snow removalDe-icing is defined as removal of snow, ice or frost from a surface...
with a type I fluid.
Chemical Composition
The main component of deicing fluid is usually propylene glycolPropylene glycol
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...
or ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
. Other ingredients vary depending on the manufacturer, but the exact composition of a particular brand of fluid is generally held as confidential proprietary information.
Based on chemical analysis, the U.S. Environmental Protection Agency has identified five main classes of additives
widely used among manufacturers:
- Benzotriazole and methyl-substituted benzotriazole, used as corrosion inhibitor/flame retardants to reduce flammability resulting from the corrosion of metal components carrying a direct current.
- AlkylphenolAlkylphenolAlkylphenols are a family of organic compounds obtained by the alkylation of phenols. The term is usually reserved for commercially important propylphenol, butylphenol, amylphenol, heptylphenol, octylphenol, nonylphenol, dodecylphenol and related "long chain alkylphenols"...
and alkylphenol ethoxylatesNonylphenolNonylphenol is a family of closely related organic compounds, a subset of the alkylphenols. This collection of compounds is a precursor to commercially important detergents...
, nonionic surfactantSurfactantSurfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
s used to reduce surface tensionSurface tensionSurface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
. - TriethanolamineTriethanolamineTriethanolamine, often abbreviated as TEA, is an organic chemical compound which is both a tertiary amine and a triol. A triol is a molecule with three alcohol groups. Like other amines, triethanolamine is a strong base due to the lone pair of electrons on the nitrogen atom. Triethanolamine can...
, used as a pH bufferBuffer solutionA buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a...
. - High molecular weight, nonlinear polymers, used to increase viscoelasticityViscoelasticityViscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just...
. - Colored dyes, such as azoAzoAzo may refer to:* Azo compound, chemistry functional group and class of compounds, also used for CDs and DVDs* A urinary tract analgesic also known as phenazopyridine* the medieval Italian jurist, see Azo of Bologna...
, xantheneXantheneXanthene is a yellow organic heterocyclic compound. Its chemical formula is 1310. It is soluble in diethyl ether. Its melting point is 101-102 °C and its boiling point is 310-312 °C...
, triphenyl methane, and anthroquinone, used to aid in identification.
The use of 1,3-propanediol
1,3-Propanediol
1,3-Propanediol is the organic compound with the formula CH22. This three-carbon diol is a colorless viscous liquid that is miscible with water.-Products:...
(a fermentation product of corn) as a base for deicing fluid was patented in 2009. At least one manufacturer of deicing fluids (Kilfrost) is now using that as a base for their product.
Usage statistics
The amount of fluid necessary to deice an aircraft depends on a wide variety of factors. Deicing a large commercial aircraft typically consumes between 500 gallons (1,892.7 l) and 1000 gallons (3,785.4 l) of diluted fluid.The cost of fluid varies widely due to market conditions. The amount deicing service companies charge end users is generally in the range of US$8 to US$12 per diluted gallon.
The total annual usage of deicing fluids in the U.S. is estimated to be approximately 25 million USgals (94,635,300 l), broken down as follows (figures from 2008, adjusted to show totals for undiluted fluid):
| Fluid type | Annual amount | Fraction |
|---|---|---|
| Type I Propylene Glycol | 19305000 US gal (73,077,378.7 l) | 77.1% |
| Type IV Propylene Glycol | 2856000 US gal (10,811,136.7 l) | 11.4% |
| Type I Ethylene Glycol | 2575000 US gal (9,747,435.9 l) | 10.3% |
| Type IV Ethylene Glycol | 306000 US gal (1,158,336.1 l) | 1.2% |
Measurement of performance
Deicing fluid performance is measured by holdover time (HOT), which is the length of time an aircraft can wait after being treated prior to takeoff. Holdover time is influenced by the ambient temperature, wind, precipitation, humidity, aircraft skin temperature, and other factors. For Type I fluids, the holdover time is only about five to 15 minutes, so the aircraft must take off immediately or else wait to be deiced again. Type IV fluids generally provide a holdover time between 30 and 80 minutes.The FAA publishes official Holdover Time Tables for all approved deicing fluids, and revises them annually.
Deicing fluids work best when they are diluted with water. For example, undiluted Dow UCAR Deicing Fluid(type I ethylene glycol), has a freezing point of −28 °C. Water, of course, freezes at 0 °C. However, a mixture of 70% deicing fluid and 30% water freezes below −55 °C. This is known as the eutectic concentration, where the freezing point of the mixture is at its lowest point, and lower than either of the component substances.
Depending on the manufacturer, deicing fluids may be sold in concentrated or pre-diluted formulations. Dilution, where necessary, must be done according to ambient weather condition and the manufacturer's instructions in order to minimize costs while maintaining safety.
The dilution of a particular sample of fluid (and hence its freezing point) can be easily confirmed by measuring its refractive index with a refractometer
Refractometer
A refractometer is a laboratory or field device for the measurement of an index of refraction . The index of refraction is calculated from Snell's law and can be calculated from the composition of the material using the Gladstone-Dale relation....
, and looking up the result in the deicing fluid manufacturer's tables.