Thursday, April 16, 2009

What is Paraffin?

In chemistry, paraffin is the common name for the alkane hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to the solids with n=20–40.

The simplest paraffin molecule is that of methane, CH4, a gas at room temperature. Heavier members of the series, such as that of octane C8H18, appear as liquids at room temperature. The solid forms of paraffin, called paraffin wax, are from the heaviest molecules from C20H42 to C40H82. Paraffin wax was identified by Carl Reichenbach in 1830.[1]
Paraffin, or paraffin hydrocarbon, is also the technical name for an alkane in general, but in most cases it refers specifically to a linear, or normal alkane — whereas branched, or isoalkanes are also called isoparaffins. It is distinct from the fuel known in Ireland, Britain and South Africa as paraffin oil or just paraffin, which is called kerosene in most of the U.S., Australia and New Zealand.
The name is derived from the Latin parum (= barely) + affinis with the meaning here of "lacking affinity", or "lacking reactivity". This is because alkanes, being non-polar and lacking in functional groups, are very unreactive.
Paraffin wax (or simply "paraffin", but see alternative name for kerosene, above) is mostly found as a white, odorless, tasteless, waxy solid, with a typical melting point between about 47 °C to 64 °C ( 116.6°F to 147.2°F), and having a density of around 0.9 g/cm3.[2] It is insoluble in water, but soluble in ether, benzene, and certain esters. Paraffin is unaffected by most common chemical reagents, but burns readily.
Pure paraffin wax is an excellent electrical insulator, with an electrical resistivity of between 1013 and 1017 ohm metre.[3] This is better than nearly all other materials except some plastics (notably teflon). It is an effective neutron moderator and was used in James Chadwick's 1932 experiments to identify the neutron.[4][5]
Paraffin wax (C25H52) is an excellent material to store heat, having a specific heat capacity of 2.14–2.9 J g–1 K–1 (joule per gram per kelvin) and a heat of fusion of 200–220 J g–1.[6] This property is exploited in modified drywall for home building material: it is infused in the drywall during manufacture so that, when installed, it melts during the day, absorbing heat, and solidifies again at night, releasing the heat.[7] Paraffin wax phase change cooling coupled with retractable radiators was used to cool the electronics of the Lunar Rover.[8] Wax expands considerably when it melts and this allows its use in thermostats for industrial, domestic and, particularly, automobile purposes.[9][10]
In industrial applications, it is often useful to modify the crystal properties of the paraffin wax, typically by adding branching to the existing carbon backbone chain. The modification is usually done with additives, such as EVA copolymers, microcrystalline wax, or forms of polyethylene. 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 for casting metal and other materials in the lost wax process, as it is relatively brittle at room temperature and presents the risks of chipping and breakage when worked. Soft and pliable waxes, like beeswax, may be preferred for such sculpture, but "investment casting waxes," often paraffin-based, are expressly formulated for the purpose.
Paraffin Wax is one of several acceptable candle waxes used in the Jewish menorah ritual.

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