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, CH
4, a gas at room temperature. Heavier members of the series, such as that of
octane C
8H
18, appear as liquids at room temperature. The solid forms of paraffin, called
paraffin wax, are from the heaviest molecules from C
20H
42 to C
40H
82. 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/cm
3.
[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.
Paraffin wax (C
25H
52) 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.
