1.Definition, procedure, advantage, and disadvantage of hydrothermal growth method of crystal. 2.Definition, procedure, advantage, and disadvantage of gel growth method of crystal.

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DISCUSSION ABOUT HYDROTHERMAL
& GEL GROWTH OF CRYSTAL
P r e p a r e d B y M d . M o s t a k i m R a h m a n ( 9 3 2 )
M Y M E N S I N G H E N G I N E E R I N G C O L L E G E

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What is hydrothermal growth of
crystal?
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Hydrothermal Growth is a process of single crystal synthesis from high
temperature aqueous solution at high vapor pressure.
The liquids from which the process starts are usually alkaline aqueous
solutions. Temperatures are typically in the range 400-600 degree C
and the pressure involved is large (100-1000 of atmospheres). Those
materials like calcite, alumina, antimony etc. can be grown by this
technique.

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Hydrothermal Crystal Growth Method
• Temperature-difference method: This is the most extensively used method
in hydrothermal synthesis and crystal growing. Supersaturation is achieved by
reducing the temperature in the crystal growth zone. The nutrient is placed in the
lower part of the autoclave filled with a specific amount of solvent. The autoclave
is heated in order to create two temperature zones. The nutrient dissolves in the
hotter zone and the saturated aqueous solution in the lower part is transported to
the upper part by convective motion of the solution. The cooler and denser
solution in the upper part of the autoclave descends while the counterflow of
solution ascends. The solution becomes supersaturated in the upper part as the
result of the reduction in temperature and crystallization sets in.
• Temperature-reduction technique: In this technique crystallization takes
place without a temperature gradient between the growth and dissolution zones.
The supersaturation is achieved by a gradual reduction in temperature of the
solution in the autoclave. The disadvantage of this technique is the difficulty in
controlling the growth process and introducing seed crystals. For these reasons,
this technique is very seldom used.
• Metastable-phase technique: This technique is based on the difference in
solubility between the phase to be grown and that serving as the starting material.
The nutrient consists of compounds that are thermodynamically unstable under the
growth conditions. The solubility of the metastable phase exceeds that of the
stable phase, and the latter crystallize due to the dissolution of the metastable
phase. This technique is usually combined with one of the other two techniques
above. 3

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ADVANTAGES & DISADVANTAGES
It occurs in air at a temperature
much lower than the melting of the
crystallizing substance.
ADVANTAGES DISADVANTAGES
Single crystals of diamond, barium
titanates are to be grown by using
this method.
At elevated temperature of crystal
growth there are some
disadvantages.
It needs expensive autoclaves and
there is impossibility of observing
the crystal as it grow.

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What is Gel growth of crystal?
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The principle used in this crystal growth techniques is very simple
solution of two suitable compounds give rise to required crystalline
substance by mere chemical reactions, crystallization takes place
according to chemical reaction equation as shown below,
X(in solution) + Gel medium Atm pressure
X(crystal)

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Various Types Of Gels
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1. Physical gel:
Gel which is obtained by Physical process such as cooling is called physical gel.
E.g.- Gelatin, clay.
2. Chemical gel:
Gels formed by chemical reaction such as hydrolysis (or) polymerization are called chemical
gels.
E.g. - Silica, Polyacryalamide.

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GEL Growth Method of Crystal
• a) Crystal growth by chemical reaction method
• b) Complex dilution method
• c) Solubility reduction method
• d) Growth by chemical reduction.
There are two types of chemical reaction method
1.Single diffusion method
2.Double diffusion method
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These procedures fall into the following categories:

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ADVANTAGES & DISADVANTAGES OF GEL GROWTH METHOD
ADVANTAGES DISADVANTAGES
1.It prevents turbulence and formation of good
crystals by providing a framework of nucleation.
2. The convection is absent in growth
experiments.
3. The high degree of perfection and lesser
number of defects have been observed in gel
growth.
4. The Gel method has also been applied to the
study of crystal formation in human system such
as cholesterol stores, Sex hormones.
1. In some crystals the gel trapping during the
growth occurs, when a silica gel is used.
2. Growth period is very long.
3. The crystal size is invariably small compared
to other methods.

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Thank You