Glossary


Abhesion

Lack of adhesion, easy release from substrates

Acetoxy Cure System

A tin catalyzed moisture cure system which generates an acetic acid/vinegar odor by-product upon curing.

Adhesive

Displaying self bonding properties without primers

Addition Cure System

Reaction between a vinyl terminated siloxane and a polyfunctional silicon hydride with a catalyst, which does not require moisture to cure.

Si-H + CH2 = CHSi ----------> SiCH2CH2Si

Application Rate

Used to measure the flow of RTV sealants from a Semco tube. Material is extruded from a Semco tube at 90 psi through a standard orifice, and is measured by grams per minute.

By-Products

The evolved reaction materials of a condensation cure silicone with moisture. These typically generate the odor found when silicones cure.

Condensation Cure System

Reaction between silanol terminated polydimethylsiloxane and multifunctional crosslinker with a catalyst.

Si-OH + AcOSi ----------> Si-O-Si + AcOH

Curing

Silicone liquids or pastes harden to a rubber elastomer

Cure Time

The time required to convert the silicone sealant to cured rubber. Example: 24 hours for 1/8” diameter bead at 77°F and 50% relative humidity.

Dimethicone

Trimethyl terminated siloxane fluid

Durometer

Resistance to indentation. Measure of the crosslink density of a rubber sample.

Elongation – (elongation at break)

The ability of the test piece to be stretched without breaking. Given in % of original dimension at maximum elongation.

Encapsulation

The complete surrounding of an electronic component or complex of components with a coating of an insulative material. The purpose is to protect the component from adverse environmental conditions.

Fast Cure

An order of magnitude faster than typical – Most room temperature cures are slow.

FIP

Form in place gasketing.

Gel Time

The period of time in which as liquid material becomes too viscous to flow or be tooled.

Heat Cured

1 or 2 part product that Vulcanizes into a hard, cured product upon exposure to heat.

Instant Cure

Heat accelerated room temperature cure within 1 minute.

Lamination

Fully enclosing an adhesive between two sheets disallowing exposure of the surface preventing offgas and surface cure. Condensation cured silicones require exposure to air for full cure, and will not work in lamination applications.

Modulus

The amount of force per square inch to stretch a test piece to a given elongation. Typically measured at 100% elongation.

Neutral Cure

A condensation cure system which liberates no corrosive (to metals) by-products upon curing. Alkoxy/Alcohol cure systems are neutral cure.

One-Part

A ready-to-use silicone material that does not require mixing with a catalyst or other additive to form a durable rubber or adhesive.

Oxime Cure System

A tin catalyzed moisture cure system which liberates an alcohol methylethylketoxime by-product upon curing. This by-product smells like latex paint.

PDMS

PolyDiMethylSiloxanes (see siloxane)

Peelable

Displaying no adhesion for easy removal

Pot Life

The amount of time available between the moment a catalyst is stirred into a base material and the approximate moment that it becomes too thick to apply in the recommended manner.

Potting Material

An electrically insulative, moisture resistant material, supplied in a liquid or putty-like form and used as a protective coating on sensitive areas of electrical and electronic equipment.

Pourable

Self-leveling liquid.

Rheology

The study of the deformation and flow of materials, in terms of stress, strain and time.

R.T.

Room temperature cure.

R.T.V.

Room temperature vulcanization (curing without heat).

Self-Leveling

A high flow, syrup-like condition, unlike thixotropic.

Silane

A highly reactive molecule having a Silicon atom as the central unit. Typically functionalized and used as crosslinkers and adhesion promoters.

Silicone Plasticizers

Trimethyl terminated siloxane fluid

Silicone Rubber

A rubber like polymer prepared from certain silicones. It maintains its elasticity and electrical properties over a wide range of temperatures and is widely used in sealants, gaskets, insulation, tapes, etc.

Siloxane Fluids

Polymers having a regular alternating silicon and oxygen central atoms, typically having pendant dimethyl functionality, these polymers can be functionalized interchain and at chain terminus for a wide range of applications.

Simethicone

Trimethyl terminated siloxane fluid

Skin-Over

The formation of an integral skin over the surface of a quantity of sealant.

Specific Gravity

The ratio of the weight of any volume of a material to the weight of an equal volume of water.

Tack-Free Time

The time it takes for a sealant to cure to a point where none of the material will stick to your finger.

Tear Resistance

Resistance to growth of a nick or cut in a test piece when tension is applied. Given in pounds per inch or Newton per millimeter.

Tensile Strength (tensile at break)

The amount of force required to break a test piece. Given in pounds per square inch(PSI) or Newton per square millimeter (N/mm2).

Two-Part

A silicone material which must be mixed with a catalyst or other additive to form a durable rubber.

Thixotropic

Non-slump or sag property, no flow without pressure

Uncured

A silicone material which has not vulcanized or formed a durable rubber.

Viscosity

The measurement of a fluid’s resistance to relative motion within itself. The viscous property of a fluid. Usually considered to be the relative thickness or thinness of a fluid as compared to the thickness (thinness) of water

Volatiles

Low molecular weight silicone materials

that can become airborne. Found in certain silicone polymers.

Work Time

The period of time which a silicone material may be “worked” before skin over and curing begins.