Sealant
Encyclopedia
A sealant may be viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary reaction. Anaerobic acrylic sealants generally referred to as impregnants are the most desirable as they are required to cure in the absence of air, unlike surface sealants that require air as part of the cure mechanisum that changes state to become solid, once applied, and is used to prevent the penetration of air, gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

, noise
Noise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...

, dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...

, fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

, smoke
Smoke
Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...

 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
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

, drywall
Drywall
Drywall, also known as plasterboard, wallboard or gypsum board is a panel made of gypsum plaster pressed between two thick sheets of paper...

, etc. Desirable properties of sealants include insolubility, corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

 resistance, and adhesion
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....

. Uses of sealants vary widely and sealants are used in many industries, for example, construction
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...

, automotive and aerospace industries.

The main difference between adhesive
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...

s 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
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...

 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 corking 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
Silicone
Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....

 is an example of a sealant.

Types of sealants

See also

  • Caulking
    Caulking
    Caulking is one of several different processes to seal joints or seams in various structures and certain types of piping. The oldest form of caulking is used to make the seams in wooden boats or ships watertight, by driving fibrous materials into the wedge-shaped seams between planks...

  • Coating
    Coating
    Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...

  • Dental sealant
    Dental sealant
    Dental sealants are a dental treatment consisting of applying a plastic material to one or more teeth, for the intended purpose of preventing dental caries or other forms of tooth decay.-Development:...

  • Seam sealant
    Seam sealant
    Seam sealants are chemical coating compositions used today in the OEM automotive industry primarily for the purpose of seals against air leaks and to waterproof sheetmetal overlaps that occur in the assembly of a vehicle. Such overlaps are typically decorative rather than structurally supportive...

  • Stone sealer
    Stone sealer
    Sealing is the application of a surface treatment to retard staining . All natural stone is porous since it is made up of countless interconnected capillary pores through which liquids and gases can move. Natural stone includes; granite, basalt, marble, limestone, travertine, sandstone and slate...

  • Varnish
    Varnish
    Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss...

  • Waterproofing
    Waterproofing
    Waterproof or water-resistant describes objects relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or under water to specified depths...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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