Seminar on "Crystal habit modification & it's industrial importance" prepared by Kishor Prajapati ( Final Year Chemical Engg. Student at Faculty of Technology & Engg.,M.S.University, Vadodara)

1. Crystal Habit Modification And It’s
Industrial Importance
Presented By: Kishor K. Prajapati
Guided By: Dr. Bina R. Sengupta

2. Introduction
 Crystallization :
Crystallization is the spontaneous arrangement of
the particles repetitative orderly, i.e.,regular
geometric patterns.
 Crystal :
A Crystal can be defined as a solid particle, which
is formed by solidification (crystallization) process
(under suitable environment) in which structural
units are arranged by a fixed geometric pattern or
lattice.
 Crystal Habit :
Crystal Habit is a description of the shapes and
aggregates that a certain mineral is likely to form.
Mullin. J.W., (1961) Crystallization (4th Edition Reprinted) Butterworth-Heinemann, ISBN O 7506

3. Different Shapes of Crystal
 Crystals can be classified into seven crystal systems :
Mullin. J.W., (1961) Crystallization (4th Edition Reprinted) Butterworth-Heinemann, ISBN O 7506

4. Crystal Habit
 The relative sizes of the faces of a particular crystal can vary considerably.
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This variation is called a modification of habit.
The crystals may grow more rapidly, or be stunted, in one direction; thus an
elonngated growth of the prismatic habit gives a needle shape crystal
(acicular habit) and a stunted growth gives a flat plate like crystal (tubular,
platy or flaky habit).
Nearly all manufactured and natural crystal are distorted to some
degree,and this frequently leads to a misunderstanging of the term
“symmetry”.
Perfect geometric symmetry is rarely observed in crystals, but
crystallographic symmetry is readily detected by means of a goniometer.
The relative growths of the faces of a crystal can be altered, and often
controlled, by a number of factors.
Rapid crystallization, such as that produced by the sudden cooling or
seeding of a supersaturated solution, may result in the formation of needle
crystals; impurities in the crystallizing solution can stunt the growth of a
crystal in certain directions; and crystallization from solutions of the given
substance in different solvents generally results in a change of habit.
The degree of supersaturation or supercooling of a solution or melt often
exerts a considerable influence on the crystal habit, and so can the state of
agitation of the system.
Mullin. J.W., (1961) Crystallization (4th Edition Reprinted) Butterworth-Heinemann, ISBN O 7506

5. A stunted growth in the vertical
direction
(or elongated growth in
the directions of the other axes) results
in a tabular crystal (a); excessively
flattened crystals are usually called
plates or flakes.
This combination-form crystal is
terminated by hexagonal pyramids and
two flat faces perpendicular to the
vertical axis; these flat parallel faces
cutting one axis are called pinacoids.
An elongated growth in the vertical
direction yields a needle or acicular
crystal (c); flattened needle crystals are
often called blades.
Mullin. J.W., (1961) Crystallization (4th Edition Reprinted) Butterworth-Heinemann, ISBN O 7506

6. Crystal habit of Potassium sulphate & Sodium
chloride
Mullin. J.W., (1961) Crystallization (4th Edition Reprinted) Butterworth-Heinemann, ISBN O 7506

7. Habit Changes in ammonium sulphate and Sodium
chloride crystals caused by traces of impurity
Mullin. J.W., (1961) Crystallization (4th Edition Reprinted) Butterworth-Heinemann, ISBN O 7506

8. Industrial Importance
 For most commercial purposes a granular or prismatic habit is usually
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desired, but there are specific occasions when other morphologies, such
as plates or needles, may be wanted.
In nearly every industrial crystallization some form of habit modification
procedure is necessary to control the type of crystal produced.
This may be done by controlling the rate of crystallization, e.g. the rate of
cooling or evaporation, the degree of supersaturation or the temperature,
by choosing a particular solvent, adjusting the solution pH, deliberately
adding an impurity that acts as a habit modifier, or even removing or
deactivating some impurity that already exists in the solution.
Surface active agents (surfactants) are frequently used to change crystal
habits.
Common anionic surfactants include the alkyl sulphates, alkane
sulphonates and aryl alkyl sulphonates.
Polymeric substances such as polyvinylalcohol, polyacrylates,
polyglutamates, polystyrene sulphonates, alginates, polyacrylamides,
etc., have also found application, as have long-chain and proteinaceous
Mullin. J.W., (1961) Crystallization (4th Edition Reprinted) Butterworth-Heinemann, ISBN O 7506
materials like sodium carboxymethylcellulose, gelatin and

9. Crystal Habit Modification
 For crystal-habit modification, crystals are grown in the presence of
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naturally occurring soluble additives, which usually adsorb or bind to
the crystal faces and influence the crystal growth or morphology.
The crystal-habit modifiers may be of a very diverse nature, such as
multivalent cations, complexes, surface active agents, soluble
polymers, biologically active macromolecules, fine particles of
sparingly soluble salts, and so on.
These crystal modifiers often adsorb selectively on to different crystal
faces and retard their growth rates, thereby influencing the final
morphology of the crystals.
Using water-soluble polymers as crystal modifiers for controlled
crystallization is widely expanding and becoming a benign route for
controlling and designing the architectures of inorganic materials.
Investigators have used polyvinylalcohol (PVA), agar-, gelatin-, and
pectin-based gel matrices to control the morphology of inorganic
crystals such as PbI2,AgI, Ag2Cr2O7,PbSO4 ,PbCl2 ,and so forth.
Among the reported common gel matrices used as crystal-habit
modifiers, PVA is a water soluble synthetic polymer with excellent
film-forming and emulsifying Edition Reprinted) Butterworth-Heinemann, ISBN O 7506
Mullin. J.W., (1961) Crystallization (4th properties.

10. Crystal Habit modification by polymers of
Copper chromite nanomaterials
 Amorphous and monodispersed copper chromite nanoparticles were
prepared by aqueous thermolysis method using PVA (Polyvinyl alcohol) and
different ratios of urea-PVA as fuel in air.
 Morphology and size of nanoparticles were measured by SEM (Scanning
electron microscopy) and TEM (Transmission electron microscopy) analysis.
 Copper chromite (CuCr2O4) is a tetragonally distorted normal spinel; this
distortion is due to Jahn Teller effect of Cu+2 ions in tetrahedral sites.
 It is a p-type semiconductor which is widely used as a catalyst for the
oxidation of CO, hydrocarbons ,alcohols and as a burn rate catalyst in
composite solid propellants, Well resolved square bipyramidal morphology
was seen in all copper chromite samples using PVA alone.
 The habit modification of copper chromite was observed due to presence of
urea.
 The urea molecule is planar in the crystal structure, but the geometry around
the nitrogen is pyramidal in the gas-phase minimum-energy structure.
 In solid urea, the oxygen center is engaged in two N-H-O hydrogen bonds.
 The resulting dense and energetically hydrogen-bond network probably
changes the morphology after combustion process.
http://www.intechopen.com/download/pdf/26216

11.  Polymer is adsorbed and acting as
bridge between particles.
 The linear chains of PVA can be cross
linked in aqueous medium .
 The cross linking between the chains
may provide small cages wherein the
“sol” of the reactant mixture gets
trapped.
 During combustion, the “sol” trapped in
the cages may get converted to
ultrafine particles of copper chromite.
 Thus cages formed by the cross
linking may offer resistance to the
agglomeration of the particles and
particle growth.
 Perfect square bipyramidal
morphology is seen in PVA capped
and orthorhombic in annealed
samples.
 Sharpness of edges decreases
http://www.intechopen.com/download/pdf/26216
gradually with increase in urea content

12.  Conclusions:
 In most of the habit modification and morphological changes of
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some inorganic materials in microsize and nanosize studies
polymers play multiple roles as a fuel in combustion synthesis,
encapsulating agent and as a habit modifier in other synthesis
method applied.
We have observed that the size, shape, morphology of the
synthesized material depends on various factors like nature of
polymer, its degree of polymerization, molecular weight,
reaction time, synthetic method applied and also on heat of
reaction.
In the methods applied at high temperature, rapid nucleation
time gives rise to short burst of nuclei which might react with
intermediate species and the reactions are more kinetically
controlled.
When the synthesis was carried out at low temperatures,
nucleation process is slow and thermodynamically driven
process. With aging, growth process becomes more favorable.
Final morphology of the material depends on equilibrium
conditions related to minimum surface energy, rate of
nucleation and growth.
Thank You