fusion Flashcards
definition
It is the process by which the solids get converted into liquids without the addition of any solvent.
The process of liquefying a substance by heat without the aid of a solvent is called fusion.
In other words, it is defined as the process of heating the solids until they melt.
explanation
In a pure crystalline solid, this process occurs at a fixed temperature called the melting point
An impure solid generally melts over a range of temperatures below the melting point of the principal
component.
Amorphous (non-crystalline) substances such as glass melt by gradually decreasing in viscosity as
temperature is raised, with no sharp transition from solid to liquid.
The structure of a liquid is always less ordered than that of the crystalline solid and, therefore, the
liquid commonly occupies a larger volume
Thermal fusion of a given mass of a solid requires the addition of a characteristic amount of heat, the
heat of fusion
In the reverse process, the freezing of the liquid to form the solid, the same quantity of heat must be
removed.
The heat of fusion of ice, the heat required to melt one gram, is about 80 calories; this amount of heat
would raise the temperature of a gram of liquid water from the freezing point (0° C, or 32° F) to 80°C
(176° F).
applications
Fusion is done to purify certain solid and semisolid substances e.g., substances like Bees wax, hard
paraffin, soft paraffin and wool fat are heated to melt and filtered while hot to remove the dissolved
impurities. Then cooling is done to obtain a product free from dissolved impurities.
This method is also applied for the preparation of ointments when they contain solids and semisolids
in the formulation. All the substances are first molted and then cooled slowly with constant stirring
until a uniform product is obtained. To avoid overheating, the substances with higher melting points
are melted first to which substances with lower melting points are added.
