What is the glass transition temperature of Aluminium?

Answer 1

it is a term concerned will polymers. At this temperature the polymer energy drops to a certain level that restricts the motion of the chains of the polymer. The polymer becomes glassy rigid after it was rubbery (very viscous liquid). The temperatur characterizes the polymer type.

Answer 2

The purer the substance the sharper and more defined the temperature at which the change (melting or boiling) occurs. As an example, a barrel of crude, oil which is a very impure substance, does not have a boiling point. Each component or fraction of the material boils at a different temperature. The Gasoline fraction boils at a lower temperature than the paraffin wax oil fraction. This is the basis of the separation and purification process which occurs at an oil refinery.

Polymeric materials by definition are not simple substances. They contain a distribution of molecular weights. In fact this is one of the key definition of polymers - a material must contain a distribution of molecular weights for it to have the definition of a polymer. It is thus an impure and non simple material. The higher the molecular weight the less defined the transition from a solid to a liquid. To complicate matters, polymers can also exist in two states -amorphous and crystalline and an infinite range in between these extremes. In the coatings industry virtually all the polymers are highly amorphous. This is from a Greek word meaning without form or shape. As an amorphous polymer is heated it does not display a sharp defined Tm.

Amorphous polymers at low temperature tend to be hard, brittle and glassy substances. As they are heated, they either melt to a viscous liquid or at higher molecular weights they change from a glassy to a rubbery state. This is called the Glass Transition Temperature - GTT or more correctly Tg (pronounced Tee sub Gee). This can easily be demonstrated by a simple experiment. Take a plastic ruler (usually made of Perspex - poly methyl methacyrlate) and bend it. There is a strong chance it will be so brittle it will snap. Now take another identical ruler and warm it gently - it will become rubbery and will no longer be hard and brittle - it has been warmed above its Glass Transition. The temperature at which this change takes place is Tg. Conversely if a soft rubber tube is placed in liquid nitrogen, it will freeze and become a brittle glassy solid and can now be shattered into many pieces.

The Tg of most of the polymers used in the coatings industry are 0 - 65 0C. As a general rule the lower the Tg the more flexible and the softer the film. Too much above its Tg and a polymer will flow slightly resulting in very poor dirt pick-up and dirt retention properties. Blocking properties will likewise be very poor.

Answer 3

It is the temperature at which a material changes from a rubbery state to glassy state. Epoxy adhesives, for example are a good example. Rubbers are also good example; for example some silicones are rubbery until -100C and then they become glassy. It is often marked by a sharp change in stiffness and expansion coefficient.

Answer 4

Glass transition temperature of any polymeric material is the temperature above that temperature material is soft and below that Tg temperature material remains hard.

Answer 5

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