Product Code Database
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. However, all common antifreeze additives also have lower heat capacity than water, and do reduce water's ability to act as a coolant when added to it.
Because water has good properties as a coolant, water plus antifreeze is used in internal combustion engines and other heat transfer applications, such as HVAC and solar water heaters. The purpose of antifreeze is to prevent a rigid enclosure from bursting due to expansion when ice. Commercially, both the additive (pure concentrate) and the mixture (diluted solution) are called antifreeze, depending on the context. Careful selection of an antifreeze can enable a wide temperature range in which the mixture remains in the liquid phase, which is critical to efficient heat transfer and the proper functioning of . Most if not all commercial antifreeze formulations intended for use in heat transfer applications include anti-corrosion and anti-cavitation agents (that protect the hydraulic circuit from progressive wear).
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 voids (pockets of steam), leading to localized hot spots and the catastrophic failure of the engine. If plain water were to be used as an engine coolant in northern climates freezing would occur, causing significant internal engine damage. Also, plain water would increase the prevalence of galvanic corrosion. Proper engine coolant and a pressurized coolant system obviate these shortcomings of water. With proper antifreeze, a wide temperature range can be tolerated by the engine coolant, such as to for 50% (by volume) propylene glycol diluted with distilled water and a 15 psi pressurized coolant system.
Early engine coolant antifreeze was methanol (methyl alcohol). Ethylene glycol was developed because its higher boiling point was more compatible with heating systems.
Another company involved in the development is BASF (Glysantin), whose standards are: G30, G40, G48, G05, G33, and G34.
Volkswagen Group:
BASF:
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 HVAC and industrial heating or cooling systems as a high-capacity heat transfer medium. Many formulations have corrosion inhibitors, and it is expected that these chemicals will be replenished (manually or under automatic control) to keep expensive piping and equipment from corroding.
are commonly used in cryobiology to prevent or inhibit freezing in sperm, blood, stem cells, plant seeds, etc. Ethylene glycol, propylene glycol, and glycerol (all used in automotive antifreeze) are commonly used as biological cryoprotectants.
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 preserve alkalinity of the solution to prevent oxidation of ethylene glycol and formation of these acids. , , and 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 ( is lethal to a person) but is much less lethal if treated within an hour.PM Leth, M Gregersen. Ethylene glycol poisoning. Forensic science international, 2005 - Elsevier (see Ethylene glycol poisoning).
Besides cooling system corrosion, biological fouling also occurs. Once bacterial slime starts to grow, the corrosion rate of the system increases. Maintenance of systems using glycol solution includes regular monitoring of freeze protection, pH, specific gravity, inhibitor level, color, and biological contamination.
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.Hartwick, D.; Hutchinson, D.; Langevin, M., "A multi-discipline approach to closed system treatment," Corrosion 2004; New Orleans, Louisiana; March 28 - April 1, 2004; NACE (National Association of Corrosion Engineers) paper 04-322. See: Document preview. 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," 2007 Annual Convention and Exposition of the Association of Water Technologies; Colorado Springs, Colorado; November 7–10, 2007Allan Browning and David Berry (September / October 2010) "Selecting and maintaining glycol based heat transfer fluids," 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.
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.
Glycerol was historically used as an antifreeze for automotive applications before being replaced by ethylene glycol. Volkswagen introduced G13 (TL 774-G) antifreezes containing glycerol in 2008, marketed as better for the environment due to its low toxicity and reduced emissions. However, since 2018, they have moved on to G12EVO (TL 774-L) which no longer contains glycerol.
Glycerol is mandated for use as an antifreeze in many sprinkler systems.
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. Propylene glycol solutions cannot be tested using specific gravity because of ambiguous results (40% and 100% solutions have the same specific gravity), 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.
DEX-COOL specifically has caused controversy. Litigation has linked it with intake manifold gasket failures in General Motors' (GM's) 3.1L and 3.4L engines, and with other failures in 3.8L and 4.3L engines. One of the anti-corrosion components presented as sodium or potassium 2-ethylhexanoate and ethylhexanoic acid is incompatible with nylon 6,6 and silicone rubber, and is a known plasticizer. Class action lawsuits were registered in several states of the US, and in Canada, to address some of these claims. The first of these to reach a decision was in Missouri, where a settlement was announced early in December 2007. Tentative Settlement of GM DEX-COOL Class Action Suit Late in March 2008, GM agreed to compensate complainants in the remaining 49 states. DEX-COOL Litigation Website GM (Motors Liquidation Company) filed for bankruptcy in 2009, which tied up the outstanding claims until a court determines who gets paid.
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". Draft—DEX 2007, Part 3: Now It’s All Up To The Judges and Juries. Imcool.com. Retrieved on 2011-01-01. DEX-COOL antifreeze uses two inhibitors: sebacate and 2-EHA (2-ethylhexanoic acid), the latter which works well with the hard water found in the United States, but is a plasticizer that can cause gaskets to leak.
According to internal GM documents, 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.
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. 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.
An example is Zerex G05, which is a low-silicate, phosphate free formula that includes the benzoate inhibitor.
A HOAT coolant can have a life expectancy as high as 10 years / 180,000 miles.
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. This dye fluoresces bright green when illuminated by blue or ultraviolet 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.VOGT, P. F. 2005. Tolyltriazole-myth and misconceptions. The Analyst 12: 1–3. These side-products are highly reactive and produce volatile aromatic amines which are responsible for the unpleasant odor.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
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: Engine Cooling Testing: Why use a refractometer? posted 2/7/2001 by Michael Reimer
Corrosion inhibitors
Most commercial antifreeze formulations include corrosion inhibiting compounds, and a colored dye (commonly a fluorescent green, red, orange, yellow, or blue) to aid in identification. Coolants Matrix 2003_5.xls. (PDF) . Retrieved on 2011-01-01. A 1:1 concentration with water is usually used, resulting in a freezing point of about , depending on the formulation. In warmer or colder areas, weaker or stronger dilutions are used, respectively, but a range of 40%/60% to 60%/40% is frequently specified to ensure corrosion protection, and 70%/30% for maximum freeze prevention down to . Peak Antifreeze chart
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 HVAC systems) are often monitored by specialist firms which take responsibility for adding corrosion inhibitors and regulating coolant composition. For simplicity, most automotive manufacturers recommend periodic complete replacement of engine coolant, to simultaneously renew corrosion inhibitors and remove accumulated contaminants.
Traditional inhibitors
Traditionally, there were two major corrosion inhibitors used in vehicles: and . American-made vehicles traditionally used both silicates and phosphates. European makes contain silicates and other inhibitors, but no phosphates. Japanese makes traditionally use phosphates and other inhibitors, but no silicates.
Organic acid technology
Most modern cars are built with organic acid technology (OAT) antifreeze (e.g., DEX-COOL Products: North America: Anti Freeze/Coolants. Havoline.com (2003-01-31). Retrieved on 2011-01-01.), or with a hybrid organic acid technology (HOAT) formulation (e.g., Zerex G-05), both of which are claimed to have an extended service life of five years or .
Hybrid organic acid technology
HOAT coolants typically mix an OAT with a traditional inhibitor, usually silicates.
Phosphate hybrid organic acid technology
P-HOAT coolants mix phosphates with HOAT. This technology is typically used in Asian makes and is often dyed red or blue.
Silicate hybrid organic acid technology
Si-OAT coolants mix silicates with HOAT. This technology is typically used in European makes and is often dyed pink.
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. 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. Because the additives in antifreeze are proprietary, the safety data sheets (SDS) provided by the manufacturer list only those compounds which are considered to be significant safety hazards when used in accordance with the manufacturer's recommendations. Common additives include sodium silicate, disodium phosphate, sodium molybdate, sodium borate, denatonium benzoate, and dextrin (hydroxyethyl starch).
Poisoning
Ethylene glycol, the main ingredient in some antifreeze, is poisonous and is considered to be very dangerous to ingest. After ethylene glycol is ingested, it is metabolism in the liver into various intermediate substances, which then get turned into oxalic acid. Oxalic acid is incredibly dangerous as it can cause, among other ailments, kidney failure, which is why a major treatment for antifreeze poisoning is Kidney dialysis to combat said kidney failure. Antifreeze is commonly consumed due to its sweet taste caused by the ethylene glycol, and is also commonly consumed as a surrogate alcohol due to its high alcohol contents. To prevent consumption due to taste, many brands have bitter additives, but many studies do not support the idea bitter additives reduce ingestions. Common symptoms of poisoning are vomiting, confusion, abdominal pain, agitation, ataxia and hematuria. Long term damage such as kidney damage, brain damage, central nervous system damage, and blindness are common.
See also
|
|
