Antifreeze
An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, allowing higher coolant temperature.[1] However, all common antifreeze additives also have lower heat capacities than water, and do reduce water's ability to act as a coolant when added to it.[2]
Because
Principles and history
Water was the original coolant for internal combustion engines. It is cheap, nontoxic, and has a high heat capacity. It however has only a 100 Kelvin liquid range, and it expands upon freezing. To address these problems, alternative coolants with improved properties were developed. Freezing and boiling points are
Use and occurrence
Automotive and internal combustion engine use
Most automotive engines are
, etc.). Water pump seal lubricant is also added.Antifreeze was developed to overcome the shortcomings of water as a heat transfer fluid.
On the other hand, if the engine coolant gets too hot, it might boil while inside the engine, causing
Early engine coolant antifreeze was methanol (methyl alcohol). Ethylene glycol was developed because its higher boiling point was more compatible with heating systems.
Other industrial uses
The most common water-based antifreeze solutions used in electronics cooling are mixtures of water and either ethylene glycol (EGW) or propylene glycol (PGW). The use of ethylene glycol has a longer history, especially in the automotive industry. However, EGW solutions formulated for the automotive industry often have silicate based rust inhibitors that can coat and/or clog heat exchanger surfaces. Ethylene glycol is listed as a toxic chemical requiring care in handling and disposal.
Ethylene glycol has desirable thermal properties, including a high boiling point, low freezing point, stability over a wide range of temperatures, and high specific heat and thermal conductivity. It also has a low viscosity and, therefore, reduced pumping requirements. Although EGW has more desirable physical properties than PGW, the latter coolant is used in applications where toxicity might be a concern. PGW is generally recognized as safe for use in food or food processing applications, and can also be used in enclosed spaces.
Similar mixtures are commonly used in
Biological antifreezes
Cryoprotectants are commonly used in cryobiology to prevent or inhibit freezing in sperm, blood, stem cells, plant seeds, etc.[5][6] Ethylene glycol, propylene glycol, and glycerol (all used in automotive antifreeze) are commonly used as biological cryoprotectants.[5][6]
Primary agents
Ethylene glycol
Most antifreeze is made by mixing distilled water with additives and a base product, usually MEG (mono ethylene glycol) or MPG (mono propylene glycol). Ethylene glycol solutions first became available in 1926 and were marketed as "permanent antifreeze" since the higher boiling points provided advantages for summertime use as well as during cold weather. They are used today for a variety of applications, including automobiles, but there are lower-toxicity alternatives made with propylene glycol available.
When ethylene glycol is used in a system, it may become oxidized to five organic acids (formic, oxalic, glycolic, glyoxalic and acetic acid). Inhibited ethylene glycol antifreeze mixes are available, with additives that buffer the pH and reserve alkalinity of the solution to prevent oxidation of ethylene glycol and formation of these acids. Nitrites, silicates, borates and azoles may also be used to prevent corrosive attack on metal.
Ethylene glycol has a bitter, sweet taste and causes inebriation. The toxic effects of ingesting ethylene glycol occur because it is converted by the liver into 4 other chemicals that are much more toxic. The lethal dose of pure ethylene glycol is 1.4 ml/kg (3 US fluid ounces (90 ml) is lethal to a 140-pound (64 kg) person) but is much less lethal if treated within an hour.[7] (see Ethylene glycol poisoning).
Propylene glycol
Besides cooling system corrosion,
Propylene glycol should be replaced when it turns a reddish color. When an aqueous solution of propylene glycol in a cooling or heating system develops a reddish or black color, this indicates that iron in the system is corroding significantly. In the absence of inhibitors, propylene glycol can react with oxygen and metal ions, generating various compounds including organic acids (e.g., formic, oxalic, acetic). These acids accelerate the corrosion of metals in the system.[9][10][11][12]
Other antifreezes
Propylene glycol methyl ether is used as an antifreeze in diesel engines. It is more volatile than glycol.[1]
Once used for automotive antifreeze, glycerol has the advantage of being non-toxic, withstands relatively high temperatures, and is noncorrosive. It is not however used widely.[1] Glycerol was historically used as an antifreeze for automotive applications before being replaced by ethylene glycol.[13][14] Volkswagen introduced G13 (TL 774-G) antifreezes containing glycerol in 2008, marketed as better for the environment due to its low toxicity and reduced CO2 emissions.[15] However, since 2018, they have moved on to G12EVO (TL 774-L) which no longer contains glycerol.[16]
Glycerol is mandated for use as an antifreeze in many sprinkler systems.[citation needed]
Measuring the freeze point
Once antifreeze has been mixed with water and put into use, it periodically needs to be maintained. If engine coolant leaks, boils, or if the cooling system needs to be drained and refilled, the antifreeze's freeze protection will need to be considered. In other cases a vehicle may need to be operated in a colder environment, requiring more antifreeze and less water. Three methods are commonly employed to determine the freeze point of the solution by measuring the concentration:[17]
- Specific gravity—(using a hydrometertest strip or some sort of floating indicator),
- Refractometer—which measures the refractive index of the antifreeze solution, and
- Test strips—specialized, disposable indicators made for this purpose.
Both specific gravity and refractive index are affected by temperature, although the former is affected much less catastrophically. Temperature compensation is nevertheless recommended for RI measurement.[17] Propylene glycol solutions cannot be tested using specific gravity because of ambiguous results (40% and 100% solutions have the same specific gravity),[17] although typical uses rarely exceed 60% concentration.
The boiling point can be similarly determined by a concentration given from one of the three methods. Datasheets for glycol/water coolant mixtures are commonly available from chemical vendors.[18]
Corrosion inhibitors
Most commercial antifreeze formulations include
Maintenance
In the absence of leaks, antifreeze chemicals such as ethylene glycol or propylene glycol may retain their basic properties indefinitely. By contrast, corrosion inhibitors are gradually used up, and must be replenished from time to time. Larger systems (such as
Traditional inhibitors
Traditionally, there were two major corrosion inhibitors used in vehicles: silicates and phosphates. American-made vehicles traditionally used both silicates and phosphates.[21] European makes contain silicates and other inhibitors, but no phosphates.[21] Japanese makes traditionally use phosphates and other inhibitors, but no silicates.[21][22]
Organic acid technology
Most modern cars are built with organic acid technology (OAT) antifreeze (e.g., DEX-COOL[23]), or with a hybrid organic acid technology (HOAT) formulation (e.g., Zerex G-05),[24] both of which are claimed to have an extended service life of five years or 240,000 km (150,000 mi).
DEX-COOL specifically has caused
According to the DEX-COOL manufacturer, "mixing a 'green' [non-OAT] coolant with DEX-COOL reduces the batch's change interval to 2 years or 30,000 miles, but will otherwise cause no damage to the engine".
According to internal GM documents,[29] the ultimate culprit appears to be operating vehicles for long periods of time with low coolant levels. The low coolant is caused by pressure caps that fail in the open position. (The new caps and recovery bottles were introduced at the same time as DEX-COOL). This exposes hot engine components to air and vapors, causing corrosion and contamination of the coolant with iron oxide particles, which in turn can aggravate the pressure cap problem as contamination holds the caps open permanently.[29]
Honda and Toyota's new extended life coolants use OAT with sebacate, but without the 2-EHA. Some added phosphates provide protection while the OAT builds up.[21] Honda specifically excludes 2-EHA from its formulas.
Typically, OAT antifreeze contains an orange dye to differentiate it from the conventional glycol-based coolants (green or yellow), though some OAT products may contain a red or mauve dye. Some of the newer OAT coolants claim to be compatible with all types of OAT and glycol-based coolants; these are typically green or yellow in color.[19]
Hybrid organic acid technology
HOAT coolants typically mix an OAT with a traditional inhibitor, usually silicates.[30]
An example is
A HOAT coolant can have a life expectancy as high as 10 years / 180,000 miles.[30]
Phosphate hybrid organic acid technology
P-HOAT coolants mix phosphates with HOAT.[30] This technology is typically used in Asian makes and is often dyed red or blue.[30]
Silicate hybrid organic acid technology
Si-OAT coolants mix silicates with HOAT.[30] This technology is typically used in European makes and is often dyed pink.[30]
Additives
All automotive antifreeze formulations, including the newer organic acid (OAT antifreeze) formulations, are environmentally hazardous because of the blend of additives (around 5%), including lubricants, buffers, and corrosion inhibitors.
Disodium fluorescein dye is added to conventional ethylene glycol formulas to visually distinguish leaked amounts from other vehicle fluids, and as a marker of type to distinguish it from incompatible types.[19] This dye fluoresces bright green when illuminated by blue or UV light from daylight or testing lamps.
Automotive antifreeze has a characteristic odor due to the additive tolyltriazole, a corrosion inhibitor. The unpleasant odor in industrial-use tolyltriazole comes from impurities in the product that are formed from the toluidine isomers (ortho-, meta-, and para-toluidine) and meta-diamino toluene which are side-products in the manufacture of tolyltriazole.[32] These side-products are highly reactive and produce volatile aromatic amines which are responsible for the unpleasant odor.[33]
See also
- Aircraft deicing fluid
- Antifreeze protein
- Air cooling
- Cryoprotectant
- Heater core
- Ice melt
- Internal combustion engine cooling
- Radiator
- Water cooling
- Waterless coolant
- Windshield washer fluid
References
- ^ ISBN 978-3527306732.
- ^ "Dispelling the Myths of Heat Transfer Fluids Presentation" (PDF). Dow Chemical Company. Retrieved 2021-06-04.
- doi:10.2210/rcsb_pdb/mom_2009_12. Archived from the originalon 2015-11-04. Retrieved 2019-08-12.
- PMID 11181960.
- ^ S2CID 4176915.
- ^ PMID 33761937.
- ^ PM Leth, M Gregersen. Ethylene glycol poisoning. Forensic science international, 2005 - Elsevier
- ISBN 92-4-120909-7.
- National Association of Corrosion Engineers) paper 04-322. See: Document preview. [permanent dead link]
- ^ Kenneth Soeder, Daniel Benson, and Dennis Tomsheck, "An on-line cleaning procedure used to remove iron and microbiological fouling from a critical glycol-contaminated closed-loop cooling water system," [permanent dead link] 2007 Annual Convention and Exposition of the Association of Water Technologies; Colorado Springs, Colorado; November 7–10, 2007
- ^ Allan Browning and David Berry (September / October 2010) "Selecting and maintaining glycol based heat transfer fluids," [permanent dead link] Facilities Engineering Journal, pages 16-18.
- ^ Walter J. Rossiter, Jr., McClure Godette, Paul W. Brown and Kevin G. Galuk (1985) "An investigation of the degradation of aqueous ethylene glycol and propylene glycol solutions using ion chromatography," Solar Energy Materials, vol. 11, pages 455-467.
- . Retrieved 2013-06-07.
- ^ "Proposed ASTM Engine Coolant Standards Focus on Glycerin". Archived from the original on 2012-11-20. Retrieved 2013-06-07.
- ^ "What you need to know about G13 antifreeze and coolant". Wolf Lubricants. Retrieved 2022-07-20.
- ^ "Approval lists". Glysantin. Retrieved 2022-07-26.
- ^ a b c Engine Cooling Testing: Why use a refractometer? Archived July 25, 2011, at the Wayback Machine posted 2/7/2001 by Michael Reimer
- ^
- ^ a b c Coolants Matrix 2003_5.xls. (PDF) . Retrieved on 2011-01-01. Archived 2008-04-16 at the Wayback Machine
- ^ Peak Antifreeze chart Archived October 5, 2010, at the Wayback Machine
- ^ a b c d e f "Coolant Confusion: It's Not Easy Being Green ... or Yellow or Orange or ..." motor.com. Retrieved 2013-06-07.
- ^ "Coolant Confusion". Archived from the original on 2013-05-12. Retrieved 2013-06-07.
- ^ Products: North America: Anti Freeze/Coolants. Havoline.com (2003-01-31). Retrieved on 2011-01-01.
- ^ "Zerex G-05® Antifreeze/Coolant". Valvoline.
- ^ "Canadian Nationwide Class Action Settlement Agreement" (PDF). Archived from the original (PDF) on 2013-05-12. Retrieved 2013-06-07.
- ^ Tentative Settlement of GM DEX-COOL Class Action Suit
- ^ DEX-COOL Litigation Website
- ^ "GM wants to dump liability for damaged engines in Dex-Cool cases". 18 November 2009. Retrieved 2013-06-07.
- ^ a b c Draft—DEX 2007, Part 3: Now It’s All Up To The Judges and Juries. Imcool.com. Retrieved on 2011-01-01.
- ^ a b c d e f "Gears Magazine - Cool It: What You Need to Know about Your Vehicle's Cooling System".
- ^ A safe and effective propylene glycol based capture liquid for fruit fly traps baited with synthetic lures – page 2|Florida Entomologist. Findarticles.com. Retrieved on 2011-01-01.
- ^ VOGT, P. F. 2005. Tolyltriazole-myth and misconceptions. The Analyst 12: 1–3.
- ^ A safe and effective propylene glycol based capture liquid for fruit fly traps baited with synthetic lures; Florida Entomologist, June, 2008 by Donald B. Thomas