WHAT IS CRYSTALLIZATION???
Crystallization is the (natural or artificial)
process of formation of solid crystals
precipitation from a solution. Crystallization is
a technique which chemists use to purify solid
compounds. Crystallization is based on the
principles of solubility: compounds (solutes)
tend to be more soluble in hot liquids
(solvents) than they are in cold liquids. If a
saturated hot solution is allowed to cool, the
solute is no longer soluble in the solvent and
forms crystals of pure compound. Impurities
are excluded from the growing crystals and
the pure solid crystals can be separated from
the dissolved impurities by filtration.
Evaporative crystallization is usually a
process that is conducted under vacuum.
This process is chosen when solubility of
the solute is nearly independent of
temperature. Special scaling problems
are not a serious problem as long as
boiling on the heater surface is avoided
by cooling method
Crystallization is based on the principles of
solubility: compounds (solutes) tend to be more
soluble in hot liquids (solvents) than they are in
cold liquids. If a saturated hot solution is
allowed to cool, the solute is no longer soluble
in the solvent and forms crystals of pure
compound. Impurities are excluded from the
growing crystals and the pure solid crystals can
be separated from the dissolved impurities by
To crystallize an impure, solid compound,
add just enough hot solvent to it to
completely dissolve it. The flask then
contains a hot solution, in which solute
molecules - both the desired compound
and impurities - move freely among the
hot solvent molecules. As the solution
cools, the solvent can no longer hold all of
the solute molecules, and they begin to
leave the solution and form solid crystals.
During this cooling, each solute molecule
in turn approaches a growing crystal and
rests on the crystal surface.
If the geometry of the molecule fits that
of the crystal, it will be more likely to
remain on the crystal than it is to go
back into the solution. Therefore, each
growing crystal consists of only one type
of molecule, the solute. After the
solution has come to room temperature, it
is carefully set in an ice bath to complete
the crystallization process. The chilled
solution is then filtered to isolate the
pure crystals and the crystals are rinsed
with chilled solvent.
Crystallization is used in manufacture step as
active pharmaceutical ingredients (APIs).
Many solutes precipitate in hydrate form at low
temperatures for example, the mass of water of
hydration to reach a stable hydrate
crystallization form is more than the available
water: A single block of hydrate solute will be
formed – this occurs in the case of calcium
It is an important application of crystallization in
food industry and manufacture of sucrose from
A decrease in temperature usually implies an
increase of the viscosity of a solution. Too high a
viscosity may give the crystallization dynamics.
It is used for purifying of drug.
A decrease in temperature usually implies an
increase of the viscosity of a solution. Too high
a viscosity may give the crystallization
Polymorphism: The ability of the same molecule
to crystallize in different structures, is
important in the manufacture of drugs and
specialty chemicals because polymorphs have
different properties. Our work aims to discover
polymorphs and control crystallization in
Amorphous solids are preferred over crystalline
solids. Organic glasses are materials for organic
electronics, bio-preservation, and delivery of
poorly soluble drugs.
Examples of natural crystallization:
There are many examples of natural process that
Geological time scale process examples
• Natural (mineral) crystal formation; Rock
Crystal is the name given to all clear colorless
quartz. It is widely used as a popular
ornamental stone and is also used as
• Snow flakes formation; Snowflakes
are a particular form of water ice.
• Honey crystallization (nearly all types
of honey crystallize).
Interesting facts about crystallization:
• Almost any solid material can crystallize—
• One thing that is not a crystal: leaded “crystal”
• The oldest known pieces of our planet’s
surface are 4.4-billion-year-old zircon crystals
from the Jack Hills of western Australia.
• The center of the earth was once thought to
be a single, 1,500-mile-wide iron crystal.
• Tiny silicate crystals, which need high
temperatures to form, have been found inside
icy comets from the solar system’s distant,
Factors affecting crystallization:
• Super saturation: super saturation is achieved by
evaporation of solvent from the solution, cooling
of solution ,production of additional solute as a
result of chemical reaction, or change in solvent
medium. Significant super saturation is required
in the absence of seed crystal.
• Time: time effect the quality of crystals produced.
Rapid rate of crystallization can result in
impurities being entrapped in the crystals.
• Rapid cooling leads to smaller crystals
while slow cooling will give larger and
better crystals. Like when you try to
make crystals in the refrigerator, the
crystals will grow faster but in smaller
pieces stuck together. But if you make
crystals in room temperature, the crystals
will grow slower larger.
• Other factors which effect
• pH, Impurities in solution, Rate of
stirring and the solvent.
• Atoms in covalent crystals are covalently
bonded with their neighbors, creating, in
effect, one giant molecule.
• Covalent solids are extendedlattice compounds, in which each atom is
covalently bonded to its nearest neighbors.
Because there are no de-localized electrons ,
covalent solids do not conduct electricity.
• Individual metal atoms of metallic
crystals site on lattice sites.
• This leaves the outer electrons of
these atoms free to float around the
lattice metallic crystals tend to be
very dense and have high melting
• The atoms of ionic crystals are held
together by electrostatic forces .
Ionic crystals are hard and have high
• Table salt (NaCl) is an example of
• The crystals contain recognizable molecules
with in their structure . Molecular crystals is
held together by non-covalent interaction like
vander wall forces or hydrogen binding.
Molecular crystals tend to be soft with
relatively low melting point.
• Example: Rock candy crystallization form of
table sugar or sucrose.
• Colour – A crystal’s colour will depend on the
different minerals used to create it and the
how the atoms within it absorb light. For
example, amethyst get its hue from iron.
2. Everyday – Despite what most people think,
‘crystals’ are found all around us. As well as
precious jewels, mundane materials such as
salt are formed through crystallisation.
• 3. Quartz – Quartz is a crystal made of silica
and oxygen and is one of the most common
minerals on Earth. It has been used in objects
like computers, watches and radios.
4. Classification – As well as being categorised
by shape, crystals can be segmented based on
their physical and chemical makeup into four
types: covalent, metallic, molecular and ionic.