is a lubricating fluid made by chemically reacting
materials of a specific chemical composition to produce a compound with
planned and predictable properties; the resulting
basestock may be supplemented with additives
to improve specific properties. Many synthetic lubricants — also called
synlubes — are derived wholly or primarily from
petrochemicals; other synlube raw materials
are derived from coal and oil shale, or are lipochemicals (from animal and
vegetable oils). Synthetic lubricants may be superior to
petroleum oils in specific performance areas.
Many exhibit higher viscosity index (V.I.),
better thermal stability and
oxidation stability, and low
volatility (which reduces oil consumption).
Most synlubes offer longer service life and, in some cases, better
biodegradability than conventional lubes; consequently, they are
increasingly being used in industrial and automotive applications.
Individual synthetic lubricants offer specific outstanding properties:
phosphate esters, for example, are fire
resistant, diesters have good oxidation stability
and lubricity, and
silicones offer exceptionally high V.I. Polyalphaolefins are
versatile lubricants with low pour points, and excellent thermal and
oxidation stability; they have good compatibility with petroleum lubricants
and most seals used with petroleum lubricants. Most synthetic lubricants can
be converted to grease by adding thickeners.
Because synthetic lubricants are higher in cost than petroleum oils, they
are used selectively where performance or safety requirements may exceed the
capabilities of a conventional oil.