From Wikipedia, the free encyclopedia
A sealant is a viscous material that changes state to
become solid, once applied, and is used to prevent the
penetration of
air,
gas,
noise,
dust,
fire,
smoke
or liquid from one location through a barrier into another.
Typically, sealants are used to close small openings that are
difficult to shut with other materials, such as
concrete,
drywall, etc. Desirable properties of sealants include
insolubility,
corrosion resistance, and
adhesion. Uses of sealants vary widely and sealants are used
in many industries, for example,
construction, automotive and aerospace industries.
The main difference between adhesives and sealants is that
sealants typically have lower strength and higher elongation
than do adhesives. Since the main objective of a sealant is to
seal assemblies and joints, sealants need to have sufficient
adhesion to the substrates and resistance to environmental
conditions to remain bonded over the required life of the
assembly. When sealants are used between substrates having
different thermal coefficients of expansion or differing
elongation under stress, they need to have adequate flexibility
and elongation. Sealants generally contain inert filler material
and are usually formulated with an elastomer to give the
required flexibility and elongation. They usually have a paste
consistency to allow filling of gaps between substrates. Low
shrinkage after application is often required. Many adhesive
technologies can be formulated into sealants.
Sealants fall between higher-strength adhesives at one end
and extremely low-strength putties and caulks at the other.
Putties and caulks serve only one function – i.e., to take up
space and fill voids. Sealants, on the other hand, despite not
having great strength, do convey a number of properties. They
seal the substrate at the glue line; they are particularly
effective in keeping moisture in or out of the components in
which they are used. They provide thermal and acoustical
insulation and may serve as fire barriers; sometimes they
contain electrical properties. They may also be used for
smoothing or filleting. In short, sealants are often called upon
to perform several of these functions at once.
No matter what the application, a sealant has three basic
functions.
1. It fills a gap between two or more substrates.
2. It forms a barrier through the physical properties of the
sealant itself and by adhesion to the substrate.
3. It maintains sealing properties for the expected lifetime,
service conditions and environments.
The sealant performs these functions by way of correct
formulation to achieve specific application and performance
properties. Unlike adhesives, however, there are not many
functional alternatives to the sealing process. Soldering or
welding can perhaps be used as a sealant in certain instances,
depending on the substrates and the relative movement that the
substrates will see in service. However, the simplicity and
reliability offered by organic elastomers usually make them the
clear choice for performing these functions.
Silicone is an example of a sealant.
Silicone
From Wikipedia, the free
encyclopedia
Not to be confused with the element
silicon.
Silicones are largely inert, man-made
compounds with a wide variety of forms and uses.
Typically heat-resistant, nonstick, and
rubberlike, they are commonly used in
cookware,
medical applications,
sealants,
adhesives,
lubricants, and
insulation.
Silicones are
polymers that include
silicon together with
carbon,
hydrogen,
oxygen, and sometimes other
chemical elements.
