Fire-resistant fluids phosphate esters

The largest volume of hydrauHc fluids are mineral oils containing additives to meet specific requirements. These fluids comprise over 80% of the world demand (ca 3.6 x 10 L (944 x 10 gal))- In contrast world demand for fire-resistant fluids is only about 5% of the total industrial fluid market. Fire-resistant fluids are classified as high water-base fluids, water-in-oil emulsions, glycols, and phosphate esters. Polyolesters having shear-stable mist suppressant also meet some fire-resistant tests. 

Liquid phosphate esters, eg, tricresyl phosphate [1330-78-5] are one of two types of fire-resistant hydraulic fluids (qv). Fire-resistant fluids account for less than 10% of the total fluids market. Phosphoms-based fluids generally are stable at high temperatures in addition to being fire resistant. Approximately 10,000 t of organophophoms compounds were used in hydraulic fluids in 1994. The manufacture of these materials consumed ca 4000 t of POCI3. 

Synthetic fire-resistant fluids have been developed to replace petroleum-based fluids for many applications. Although there are several types of these less hazardous fluids, the only synthetic fluids discussed in this profile are phosphate esters and polyalphaolefins. The phosphate esters are tertiary esters of orthophosphoric acid, 0=P(0H)3, and may be triaryl, trialkyl, and alkyl/aryl. The polyalphaolefins are usually based on 2-decene and contain a mixture of oligomers (dimers, trimers, etc.). 

Hydraulic fluids used close to a potential source of ignition such as a hot surface are a serious fire hazard. In such circumstances, phosphate esters are used particularly for their inherent fire resistance and where their moderate cost can be borne. Fire-resistant hydraulic fluids are the largest volume use of phosphate esters in addition they give lubrication equal to that of formulated hydrocarbon fluids. Other requirements such as viscosity or thermal stability can be met by appropriate choice of substituents. Industrial fire-resistant fluids are often required to operate at sustained... 

The pumping unit is the source of the pressurized hydraulic fluid used to power the press. Most hydraulic presses are designed to operate on petroleum-based hydraulic fluid. Where the possibility of fire is a concern, fire retardant and fire-resistant fluids are available however, certain fluids such as phosphate ester and high-water-base fluids will require special design considerations regarding their use. The pumping unit typically consists of a reservoir on which are mounted the essential hydraulic components ... 

Other Fire-Resistant Hydraulic Fluids. Phosphate and more recently polyol esters are marketed as fire-resistant compounds. They are formulated with additives to control wear, oxidation, corrosion, and misting. Seal compatibdity and solvency characteristics of these fluids may be quite different from those of mineral ods. 

Halogenated hydrocarbons that are inexpensive sometimes are used alone or in blends with phosphate esters as fire-resistant hydrauHc fluids. Other halogenated fluids are used for oxygen-compressor lubricants, lubricants for vacuum pumps that are in contact with corrosive materials, solvent-resistant lubricants, and other lubricant appHcations where highly corrosive or reactive materials are being handled. 

Phosphate ester fluids are the most fire resistant of moderately priced lubricants, are generally excellent lubricants, and are thermally and oxidatively stable up to 135°C (38). Fire-resistant iadustrial hydrauHc fluids represent the largest volume commercial use. AppHcations are made ia air compressors and continue to grow for aircraft use (tributyl and/or an alkyl diaryl ester) and ia hydrauHc control of steam turbiaes ia power generation (ISO 46 esters). 

Organophosphate Ester Hydraulic Fluids. Organophosphate ester hydraulic fluids are used in applications that require a degree of fire resistance such as in aircraft. EPA (1992b) has noted that aircraft mechanics may have dermal exposures of 1,300-3,900 mg/day and that 2,200 aircraft workers are routinely exposed to tributyl phosphate, while another 43,000 mechanics may be exposed at various times. Estimates of worker exposure in other industries were not found in the available literature. General population and military personnel exposure to organophosphate ester hydraulic fluids is likely to be much lower than exposure to mineral oil hydraulic fluids because these fluids have more specialized uses. 

Others Phosphate esters Silicone oils Halogenated fluids Polyphenyl ethers Fire resistant hydraulic fluids, gas turbine oils High temperature hydraulic fluids, brake fluids, compressor oils Extremely fire-resistant hydraulic oils Radiation-resistant, heat transfer fluids... 

Phosphate ester (e.g., Fyrquel ) Has a higher flash point than hydrocarbon oils and is considered fire-resistant, not fireproof. Its use was more common until the advent of fluorocarbon fluids. Reacts slowly with water from water vapor when in use, causing a decrease in potential vacuum. Thus it is necessary to change the pump oil more often than would be required with hydrocarbon oils. 

Phosphate esters have been produced commercially since the 1920s and now have important applications as plasticisers, lubricant additives and synthetic-based fluids for hydraulic and compressor oils. Their first use in lubrication was as anti-wear additives. Later developments in aircraft hydraulic control systems, particularly during the Second World War, introduced phosphate esters as less flammable hydraulic fluids. As esters of orthophosphoric acid they have the general formula OP(OR)3, where R represents an aryl or an alkyl group or, very often, a mixture of alkyl and/or aryl components. The physical and chemical properties of phosphate esters can be varied considerably depending on the choice of substituents [59, 60], selected to give optimum performance for a given application. Phosphate esters are particularly used in applications that benefit from their excellent fire-resistant properties, but compared to other base fluids they are fairly expensive. 

The low-temperature fluidity requirements of the applications in which this fluid is used mandate a base oil of a relatively light nature which results in a low flash point. The specification requirement is 81°C minimum using the Pensky-Martens closed (PMC) method [22]. The US military concerns for the flammability of this fluid led to the requirement for a less flammable hydraulic fluid. Civil aircraft of the period were already using phosphate ester-based hydraulic fluids because of their fire resistance. But their very different chemistry meant they were incompatible with hydraulic systems developed for the mineral-type fluid and conversion of those systems to accommodate the phosphate ester fluid was considered too expensive. 

Because of concerns in the 1940s over the flammability of mineral and vegetable oil-based hydraulic fluids the civil aviation industry sought a fluid with greater fire resistance. The result was the introduction of a phosphate ester-based hydraulic fluid. These fluids contain in the region of 90% phosphate ester and are of the general structure (R0)3P=0, where R = butyl or isobutyl. 

There are two broad categories of phosphate esters, triaryl phosphate and trialkyl phosphate. Although triaryl phosphate-based fluids have superior fire resistance and oxidative stability, the trialkyl phosphates have better viscosity/temperature properties, low temperature viscosity and lower density [26]. Low temperature viscosity and fluid density are major considerations for aircraft designers and excellent low temperature viscosity characteristics are critical for worldwide operational... 

SAE AS 1241. Fire Resistant Phosphate Ester Hydraulic Fluid for Aircraft. SAE International. Williams A. (2007) Specifying an Aircraft Lithium Soap - Tapered Roller - Wheel Bearing Grease. Manager General Mechanical Systems Engineering, Airbus. Presented at the ELGI AGM, May 2007. 

Recognition that heat stabilization of the plasticizer as well as the PVC resin was necessary greatly assisted researchers working on the problem. Epoxy compounds perform both functions. Today, they are part of many stabilization systems for vinyl compositions, so much so that worldwide use approaches 400 million pounds. In addition to vinyl stabilization, they are also used in phosphate ester functional fluids (i.e., fire-resistant hydraulic fluids) where acid development must also be avoided. 

Phosphate esters are produced from phosphorus oxychloride with various alcohols or phenols, or combinations of these hydroxyl compounds. These fluids generally have good thermal and oxidative stabilities and fire-resistancy. However, because of their high polarity, poor Vl-pour point balance, facile hydrolysis and inferior elastomer and paint compatibility, their use in general lubrication is limited. The major use for phosphate esters is in fire-resistant hydraulic oils. 

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