Antifreeze

=__Antifreeze:__= Antifreeze is a freeze preventive used in internal combustion engines and other heat transfer applications such as HVAC chillers and solar water heaters. The purpose of antifreeze is to prevent a rigid enclosure from undergoing catastrophic deformation due to expansion when water turns to ice. Antifreezes are chemical compounds added to water to reduce the freezing point of the mixture below the lowest temperature that the system is likely to encounter. Either the //additive// or the //mixture// may be referred to as antifreeze. An antifreeze mixture often achieves freezing-point depression for a cold environment and also achieves boiling-point elevation to enable higher liquid temperatures. This is described as the action of a colligative agent, which can properly be referred to as both antifreeze and "anti-boil" when used for both properties. 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 heat exchangers.

The main component in Antifreeze is a chemical known as ethylene glycol. Pure ethylene glycol freezes at around -12 degrees Celsius. However, when the ethylene glycol is mixed in a 60:40 ratio with water, it disrupts the hydrogen bonding and neither of the liquids can properly form a crystal structure; depreciating the freezing point to ~45 degrees Celsius. Due to the extremely low freezing point, it is resistant to freezing under most earthly conditions, making it highly effective in the use in automobiles and other potentially cold conditioned machinery uses.

**__Uses of Antifreeze__**
Antifreeze used in automobiles lubes the water pump, increases the boiling point, and decreases the freezing point of the cooling system. Meaning that it is used in the coolant system of your car to keep your engine block from freezing of overheating. It is extremely useful on a cold day in the mountains!



Automotive and internal combustion engine use
Most automotive engines are "water"-cooled to remove waste heat, although the "water" is actually antifreeze/water mixture and not just plain water. The term //engine coolant// is widely used in the automotive industry, which covers its primary function of convective heat transfer for internal combustion engines. When used in an automotive context, corrosion inhibitors are added to help protect vehicles' radiators, which often contain a range of electrochemically incompatible metals (aluminum, cast iron, copper, brass, solder, et cetera). Water pump seal lubricant is also added. Antifreeze was developed to overcome the shortcomings of water as a heat transfer fluid. In some engines freeze plugs are placed in areas of the engine block where coolant flows in order to protect the engine from freeze damage if the ambient temperature drops below the freezing point of the antifreeze/water mixture. These should not be confused with core plugs whose purpose is to allow removal of sand used in the casting process of engine blocks (core plugs will be pushed out if the coolant freezes, though). 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, it would promote galvanic corrosion. Proper engine coolant and a pressurized coolant system can help obviate the problems which make plain water incompatible with automotive engines. With proper antifreeze a wide temperature range can be tolerated by the engine coolant, such as −34 °F (−37 °C) to +265 °F (129 °C) for 50% (by volume) propylene glycol diluted with water and a 15 psi pressurized coolant system.[1][2] Early engine coolant antifreeze was methanol (methyl alcohol), still used in windshield washer fluid. As radiator caps were vented, not sealed, the methanol was lost to evaporation, requiring frequent replenishment to avoid freezing of the coolant. Methanol also accelerates corrosion of the metals, especially aluminium, used in the engine and cooling systems. Ethylene glycol was developed, and soon replaced methanol as an engine cooling system antifreeze. It has a very low volatility compared to methanol and to water.

Other uses
The most common water-based antifreeze solutions is 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. The use of PGW as a coolant is becoming more common primarily because it is environmentally friendly and non-toxic. 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.

Primary agents
Most antifreeze is made by mixing distilled water with some kind of alcohol.

Methanol
Methanol (also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits) is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colorless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). At room temperature, it is a polar solvent and is used as an antifreeze, solvent, fuel, and as a denaturant for ethyl alcohol. It is not popular for machinery, but may be found in automotive windshield washer fluid, de-icers, and gasoline additives.

Ethylene glycol
Ethylene glycol solutions 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.

Poisoning
Ethylene glycol is toxic to humans and animals and should therefore be handled and disposed of properly. It has a sweet taste that can contribute to its accidental ingestion and it's use as a poison. Such poisoning is difficult to identify without specialized testing, as it often mimics other illnesses, and various symptoms can result from such poisoning, including severe diarrhea and vomiting. Some ethylene glycol antifreeze contains an embittering agent such as denatonium to help discourage either accidental or deliberate consumption.

Propylene glycol
Propylene glycol, on the other hand, is considerably less toxic than ethylene glycol and may be labeled as "non-toxic antifreeze". It is used as antifreeze where ethylene glycol would be inappropriate, such as in food-processing systems or in water pipes in homes where incidental ingestion may be possible. Propylene glycol oxidizes when exposed to air and heat, forming lactic acid.[8][9] If not properly inhibited, this fluid can be very corrosive, so pH buffering agents are often added to propylene glycol, to prevent acidic corrosion of metal components. Besides cooling system breakdown, biological fouling also occurs. Once bacterial slime starts, 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.

Glycerol
Once used for automotive antifreeze, glycerol has the advantage of being non-toxic, suppresses bacterial growth, withstands relatively high temperatures, and is noncorrosive. Like ethylene glycol and propylene glycol, glycerol is a non-ionic kosmotrope that forms strong hydrogen bonds with water molecules, competing with water-water hydrogen bonds. This disrupts the crystal lattice formation of ice unless the temperature is significantly lowered. The minimum freezing point temperature is at about −36 °F / −37.8 °C corresponding to 60–70% glycerol in water.[10] Glycerol was historically used as an antifreeze for automotive applications before being replaced by ethylene glycol, which has a lower freezing point. While the minimum freezing point of a glycerol-water mixture is higher than an ethylene glycol-water mixture, glycerol is not toxic and is being reexamined for use in automotive applications.[11][12] Glycerol is mandated for use as an antifreeze in many sprinkler systems. In the laboratory, glycerol is a common component of solvents for enzymatic reagents stored at temperatures below 0 °C due to the depression of the freezing temperature of solutions with high concentrations of glycerol. It is also used as a cryoprotectant where the glycerol is dissolved in water to reduce damage by ice crystals to laboratory organisms that are stored in frozen solutions, such as bacteria, nematodes, and mammalian embryos.

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 radiator 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: Although ethylene glycol hydrometers are widely available and mass-marketed for antifreeze testing, they give false readings at high temperatures because specific gravity changes with temperature. Propylene glycol solutions cannot be tested using specific gravity because of ambiguous results (40% and 100% solutions have the same specific gravity).
 * 1) Specific Gravity— (using a hydrometer or some sort of floating indicator),
 * 2) Refractometer— which uses the optical properties of the solution, and
 * 3) Test strips— specialized, disposable indicators made for this purpose.

Corrosion Inhibitors
Most commercial antifreeze formulations include corrosion inhibiting compounds, and a colored dye (commonly a green, red, orange, yellow, or blue fluorescent) to aid in identification. A 1:1 dilution with water is usually used, resulting in a freezing point of about −34 °F (−37 °C), 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 −84 °F (−64 °C).

Traditional inhibitors
Traditionally, there were two major corrosion inhibitors used in vehicles: silicates and phosphates. American made vehicles traditionally used both silicates and phosphates.European makes contain phosphates and other inhibitors, but no silicates. Japanese makes traditionally use phosphates and other inhibitors, but no silicates.

What is in Antifreeze: Antifreeze is a substance added to a solvent, such as water, to lower its freezing point. Antifreeze is typically added to water in the cooling system of an internal-combustion engine so that it can be cooled below the freezing point of pure water (32 degrees F) without freezing. Ethylene glycol is the most widely used automotive cooling-system antifreeze, although methanol, ethanol, isopropyl alcohol, and propylene glycol are also used. In automotive windshield-washer fluids, an alcohol (e.g., methanol) is usually added to keep the mixture from freezing; it also acts as a solvent to help clean the glass. The brine used in some commercial refrigeration systems is an antifreeze mixture; it is typically a water solution of calcium chloride or propylene glycol.

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