growth of copper (1)

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Growth of Copper (II) Sulphate Pentahydrate

(CuSO4 5H2O) from Aqueous Solution

Tutor:Hess

Student:

Jingwei Wang Nr.3557579


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Abstract:

Crystal growth of CuSO4 5H2O from an aqueous

solution by means of the temperature reduction method


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Content


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1.Introduction1.1 Methods of crystal growth

Methods of crystal growth consist of simple cheap techniques

and complex process relatively. The growth time for

crystallization varies. Crystals may be produced in the solid,

liquid or vapour phase.On this basis, methods of crystal growth

can be sorted into three categories below,

Solid Growth - Solid-to-Solid phase transformation

Liquid Growth - Liquid to Solid phase transformation

Vapour Growth - Vapour to Solid phase transformation

Based on the phase transformation process, crystal growth

techniques are classified as solid growth, vapour growth, melt

growth and solution growth (Pamplin 1979).

1.2 Growth from solution

Materials, which possess high solubility and have variation in

solubility with temperature can be grown easily by solution

method. This method is simpler and cheaper compared with

other methods. But growth process is slow and it takes a long

time for crystallization. There are several methods in solution

growth depending on the solvents and the solubility of the

solute. They are


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1 Temperature reduction method

2 Isothermal evaporation method

3salting out

1.2.1 Temperature reduction method

This method is applicable to those crystals which possess a

higher solubility constant and a certain temperature range. And

this range is limited: The upper limit supposed to not be too high

due to more evaporation. Too lower limit will be disadvantage

of crystal growth. Generally, the starting point should be

50~60,the reduction range should be 15~20. It is better that

the solubility of crystal via this method not be lower than

1.5g/1000g* . During whole growth process, the key is to

control suitable temperature reduction rate which enable

solution to stay in metastable area.

2.Theory

2.1Ostwalds Diagram

The relationship between temperature of spontaneous

crystallization and solubility is shown by the dashed , called

supersolubility curve. The significance of this curve is not as

clear as solubility curve due to external factor effection.

The three areas are stable, metastable and labile separately.


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(1) In stable area, it is impossible to crystallize.

(2) In metastable area, spontaneous crystallization doesnt occur.

But crystal growth is possible if seed crystals exist.

(3) In labile area, spontaneous crystallization is possible but not

inevitable. But it may generate many seed crystals

instantaneously.

Figure 2.1Ostwald-Miers diagram for a solute/solvent system

2.2Nucleation and Growth Kinetics

The accomplishment of supersaturation is not able to start

crystallization. The formation of nuclei with a number of minute

solid particles present in the solution is a prerequisite. Then

nucleation may occur spontaneously.

The formation of nuclei can be sorted by homogeneous and


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heterogeneous.

2.2.1 Homogeneous nucleation

The liquid structure is disorder from long rang, but unstable in

short range, which means possessing some ordered atom group.

When temperature reduces below melting point, these ordered

atom group are possible to form embryo. So when embryo

emerge in supercooling liquid, on one hand, the atom inside are

ordered and possess a lower Gibbs free energy, which drive

phase change. One the other hand, formation of new embryo

generates more surface which increase surface free energy.

Thats the resistance. So the sum change in free energy G is:

G reaches maximum value when radius is r*.See in Fig.2.2.1.

When rr*, the growth of nuclei

reduce free energy. These embryos are stable ones.


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Fig.2.2.1

2.2.2Heterogeneous nucleation

Heterogeneous nucleation occurs much more often than

homogeneous nucleation. Usually, it forms in phase boundaries

or sticks on impurities like dust and wall. The initial energy is

less than that of homogeneous nucleation. At such

heterogeneous phase, the effective surface energy is lower. The

more infiltrated they are, the less energy for facilitating

nucleation and is the lower nuclear barrier is.

3.Growth Process3.1Cleaning

First clean all the apparatus which mentioned in the scription.


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3.2Growth of seed crystals

Preparation of solution:

Prepare 30 g CuSO 5 H O with 100 ml 18 Mcm H O in a 300

ml cooking cup.

Dissolve the CuSO 5 H O at about 50 C under stirring (on

heating plate). If a residue remains one can


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a) add 18 Mcm H O,2

b) heat a little more, or

c) filter it out.

Let it stay over night at room temperature (there should be

some crystals formed, see Fig. 3).

3.2 Preparation of Saturated Solution

3.3Determination of the Saturation Point of the Solution

By Schlieren Method, we can find out the saturated point using

seed crystal with cord.

The principles are as follows:


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growth of copper (1)

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