Silicone grease, sometimes called dielectric grease, is a waterproof
grease made by combining a
silicone oil
A silicone oil is any liquid polymerized siloxane with organic side chains. The most important member is polydimethylsiloxane. These polymers are of commercial interest because of their relatively high thermal stability, lubricating, and dielect ...
with a thickener. Most commonly, the silicone oil is
polydimethylsiloxane (PDMS) and the thickener is
amorphous
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal.
Etymology
The term comes from the Greek language, Gr ...
fumed silica
Fumed silica (CAS_Registry_Number, CAS number 112945-52-5), also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary partic ...
. Using this formulation, silicone grease is a translucent white viscous paste, with exact properties dependent on the type and proportion of the components. More specialized silicone greases are made from fluorinated silicones or, for low-temperature applications, PDMS containing some
phenyl substituents in place of methyl groups. Other thickeners may be used, including
stearates and powdered
polytetrafluorethylene
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemour ...
(PTFE). Greases formulated from silicone oils with silica thickener are sometimes referred to as silicone paste to distinguish them from silicone grease made with silicone oil and a soap thickener.
Applications
Industrial use
Silicone grease is commonly used for lubricating and preserving many types of rubber parts, such as
O-rings, without swelling or softening the rubber, but is contraindicated for silicone rubber due to these factors. It functions well as a
corrosion inhibitor and lubricant on non-metal-metal contact areas.
Silicone grease is soluble in organic solvents such as
toluene
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) ...
,
xylene
In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are s ...
,
mineral spirits, and
chlorinated hydrocarbons. It is insoluble in
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is ...
,
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
, and water.
Thermal grease
Thermal paste (also called thermal compound, thermal grease, thermal interface material (TIM), thermal gel, heat paste, heat sink compound, heat sink paste or CPU grease) is a thermally conductive (but usually electrically insulating) chemi ...
often consists of a silicone-grease base, along with added thermally conductive fillers. It is used for heat-transfer abilities, rather than friction reduction.
Pure silicone grease is widely used by the plumbing industry in faucets and seals, as well as in dental equipment. This is due to it not being an ingestion hazard. Electrical utilities use silicone grease to lubricate separable elbows on lines that must endure high temperatures. Silicone greases generally have an
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
range of approximately with some high-temperature versions extending this range slightly.
Chemical laboratories
Silicone grease is widely used as a temporary sealant and a lubricant for interconnecting
ground glass joint
Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from interchangeable commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints ...
s, as is typically used in
laboratory glassware. Although silicones are normally assumed to be chemically inert, several historically significant compounds have resulted from unintended reactions with silicones. The first salts of
crown ethers (OSi(CH
3)
2)
''n'' were produced by reactions of organolithium and organopotassium compounds with silicone greases or the serendipitous reaction of stannanetriol with silicone grease to afford a cage-like compound having three Sn−O−Si−O−Sn linkages in the molecule.
Lubrication of an apparatus with silicone grease may result in the reaction mixture being contaminated with the grease. The impurity may be carried through purification by
chromatography in undesirable amounts. In
NMR spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic fi ...
, the methyl groups in polydimethylsiloxane display
1H and
13C chemical shifts similar to
trimethylsilane (TMS), the reference compound for those forms of NMR spectroscopy. As with TMS, the signal is a singlet. In
1H NMR, silicone grease appears at a singlet at δ = 0.07 ppm in CDCl
3, 0.09 in CD
3CN, 0.29 in C
6D
6, and −0.06 ppm in (CD
3)
2SO. In
13C NMR, it appears at δ = 1.19 ppm in CDCl
3 and 1.38 ppm in C
6D
6. Tables of impurities commonly found in NMR spectroscopy have been prepared, and such tables include silicone grease.
Consumer products
Silicone-based lubricants are often used by consumers in applications where other common consumer lubricants, such as
petroleum jelly, would damage certain products, such as latex rubber and gaskets on dry-suits. It can be used to lubricate fountain pen filling mechanisms and threads. It is used to seal and preserve O-rings in
flashlight
A flashlight (American English, US, Canadian English, Canada) or torch (British English, UK, Australian English, Australia) is a portable hand-held electric lamp. Formerly, the light source typically was a miniature incandescent light bulb, b ...
s, plumbing, waterproof watches, and air rifles. Silicone grease is widely used to lubricate threads of water-submersible flashlights used for diving and spearfishing. This grease improves water resistance of the flashlights and protects threads from wearing out. Silicone grease is used with waterproof devices, as it has a very thick body and doesn't dissolve in water as most spirits and other liquids would. Another common use is to lubricate keyboard stabilizer wires two reduce rattle.
Electrics
Silicone greases are electrically
insulating and are often applied to
electrical connectors, particularly those containing rubber gaskets, as a means of sealing and protecting the connector. In this context they are often referred to as
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the ma ...
grease.
A common use of this type is in the high-voltage connection associated with gasoline-engine spark plugs, where grease is applied to the rubber boot of the plug wire to help it slide onto the ceramic insulator of the plug, to seal the rubber boot, and to prevent the rubber's adhesion to the ceramic. Such greases are formulated to withstand the high temperature generally associated with the areas in which spark plugs are located, and can be applied to contacts as well (because the contact pressure is sufficient to penetrate the grease film). Doing so on such high-pressure contact surfaces between different metals has the further advantage of sealing the contact area against electrolytes that might cause rapid deterioration of the metals by
galvanic corrosion.
Silicone grease can decompose to form an insulating layer at or next to switch contacts that experience
arcing, and contamination can cause the contacts to prematurely fail.
SCUBA Diving
Silcone greases, of formulas qualified for such use, are often used for lubrication in the
SCUBA
Scuba may refer to:
* Scuba diving
** Scuba set, the equipment used for scuba (Self-Contained Underwater Breathing Apparatus) diving
* Scuba, an in-memory database developed by Facebook
* Submillimetre Common-User Bolometer Array, either of two in ...
industry. e.g. For lubricating components of gas pressure regulation and delivery equipment such as
regulators,
'O' rings and couplings.
Divers use high
PO2 'enriched' gas mixes containing more than the usual ~21% of
Oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
present in air as one of the ways to reduce the risk of
decompression sickness, "the bends", on certain types of dive. Also, oxygen equipment between 60% and 100% is used to
'accelerate' decompression obligations. Silicone grease is used due to the risk that some non-silicone greases can
spontaneously combust
Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high tem ...
in the presence of high concentrations of oxygen.
References
{{Reflist
Silicones
Greases