Paraffin wax (orpetroleum wax) is a soft colorless solid derived frompetroleum,coal, oroil shale that consists of a mixture ofhydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature andbegins to melt above approximately 37 °C (99 °F),[2] and its boiling point is above 370 °C (698 °F).[2] Common applications for paraffin wax includelubrication,electrical insulation, andcandles;[3] dyed paraffin wax can be made intocrayons.
Un-dyed, unscented paraffin candles are odorless and bluish-white. Paraffin wax was first created byCarl Reichenbach in Germany in 1830 and marked a major advancement in candlemaking technology, as it burned more cleanly and reliably thantallow candles and was cheaper to produce.[4]
In chemistry,paraffin is used synonymously withalkane, indicating hydrocarbons with the general formula CnH2n+2. The name is derived fromLatinparum ("very little") +affinis, meaning "lackingaffinity" or "lackingreactivity", referring to paraffin's unreactive nature.[5]
Paraffinwax is mostly found as a white, odorless, flavourless, waxy solid, with a typical melting point between about 46 and 68 °C (115 and 154 °F),[6] and a density of around 900 kg/m3.[7] It is insoluble in water, but soluble inether,benzene, and certainesters. Paraffin is unaffected by most common chemicalreagents butburns readily.[8] Its heat of combustion is 42 MJ/kg.[9]
The hydrocarbonC31H64 is a typical component of paraffin wax.
Paraffin wax is an excellent material forstoring heat, with aspecific heat capacity of 2.14–2.9 J⋅g−1⋅K−1 (joules pergram perkelvin) and aheat of fusion of 200–220 J⋅g−1.[13] Paraffin wax phase-change cooling coupled with retractable radiators was used to cool the electronics of theLunar Roving Vehicle during the crewed missions to the Moon in the early 1970s.[14] Wax expands considerably when it melts and so is used inwax elementthermostats for industrial, domestic and, particularly, automobile purposes.[15][16]
If pure paraffin wax melted to the approximate flash point in a half open glass vessel which is then suddenly cooled down, then its vapors may autoignite as result of reachingboiling liquid pressure.[17]
Paraffin wax was first created in 1830 by German chemistKarl von Reichenbach when he attempted to develop a method to efficiently separate and refine waxy substances naturally occurring in petroleum. Paraffin represented a major advance in the candle-making industry because it burned cleanly and was cheaper to manufacture than other candle fuels such asbeeswax andtallow. Paraffin wax initially suffered from a low melting point. This was remedied by addingstearic acid. The production of paraffin wax enjoyed a boom in the early 20th century due to the growth of the oil and meatpacking industries, which created paraffin and stearic acid as byproducts.[4]
The feedstock for paraffin isslack wax, which is a mixture of oil and wax, a byproduct from the refining of lubricating oil.
The first step in making paraffin wax is to remove the oil (de-oiling or de-waxing) from the slack wax. The oil is separated by crystallization. Most commonly, the slack wax is heated, mixed with one or moresolvents such as aketone and then cooled. As it cools, wax crystallizes out of the solution, leaving only oil. This mixture is filtered into two streams: solid (wax plus some solvent) and liquid (oil and solvent). After the solvent is recovered by distillation, the resulting products are called "product wax" (or "press wax") and "foots oil". The lower the percentage of oil in the wax, the more refined it is considered to be (semi-refined versus fully refined).[18] The product wax may be further processed to remove colors and odors. The wax may finally be blended together to give certain desired properties such as melt point and penetration. Paraffin wax is sold in either liquid or solid form.[19][20][21]
In industrial applications, it is often useful to modify the crystal properties of the paraffin wax, typically by addingbranching to the existing carbon backbone chain. The modification is usually done with additives, such asEVA copolymers,microcrystalline wax, or forms ofpolyethylene. The branched properties result in a modified paraffin with a higher viscosity, smaller crystalline structure, and modified functional properties. Pure paraffin wax is rarely used for carving original models forcasting metal and other materials in thelost wax process, as it is relatively brittle at room temperature and presents the risks of chipping and breakage when worked. Soft and pliable waxes, likebeeswax, may be preferred for such sculpture, but "investment casting waxes," often paraffin-based, are expressly formulated for the purpose.
In a histology or pathology laboratory, paraffin wax is used to impregnate tissue prior to sectioning thin samples. Water is removed from the tissue through ascending strengths of alcohol (75% to absolute), and then the alcohol is cleared in an organic solvent such asxylene. The tissue is then placed in paraffin wax for several hours, then set in a mold with wax to cool and solidify. Sections are then cut on amicrotome.
Anti-caking agent, moisture repellent, and dustbinding coatings forfertilizers
Antiozonant agents: blends of paraffin and micro waxes are used in rubber compounds to preventcracking of the rubber; the admixture of wax migrates to the surface of the product and forms a protective layer. The layer can also act as arelease agent, helping the product separate from itsmould.[22]
^abFreund, Mihály; Mózes, Gyula (1982).Paraffin products: properties, technologies, applications. Translated by Jakab, E. Amsterdam, the Netherlands: Elsevier. p. 121.ISBN978-0-444-99712-8.
^Nasser, William E (1999). "Waxes, Natural and Synthetic". In McKetta, John J (ed.).Encyclopedia of Chemical Processing and Design. Vol. 67. New York: Marcel Dekker. p. 17.ISBN978-0-8247-2618-8. This can vary widely, even outside the quoted range, according to such factors as oil content and crystalline structure.
^Seager, Spencer L.; Slabaugh, Michael (19 January 2010). "Alkane reactions".Chemistry for Today: General, Organic, and Biochemistry. Belmont, California: Cengage. p. 364.ISBN978-0-538-73332-8.
^"Electrical insulating materials".Kaye and Laby Tables of Physical and Chemical Constants. National Physical Laboratory. 1995. Archived fromthe original on 27 September 2007. Retrieved25 October 2013.
^"Specific Heat Capacity".Diracdelta.co.uk Science and Engineering Encyclopedia. Dirac Delta Consultants Ltd, Warwick, England. Archived fromthe original on 4 August 2007. Retrieved25 October 2013.
^Dean, W. G.; Karu, Z. S. (February 1993). "Space Station thermal storage/refrigeration system research and development".Final Report Lockheed Missiles and Space Co.
^abBodén, Roger."Paraffin Microactuator"(PDF).Materials Science Sensors and Actuators. University of Uppsala. Archived fromthe original(PDF) on 8 February 2012. Retrieved25 October 2013.
