growth of copper real (autosaved)

7/29/2019 Growth of Copper Real (Autosaved)

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Growth of Copper (II) SulphatePentahydrate

(CuSO4.5H2O) from Aqueous Solution.

Introduction

Crystals play an important role in modern technology and their importance in the field of

pharmaceutical, agriculture and materials science cannot be over emphasized. The physical

and chemical properties of crystals determine their uses. Usually crystal growth aims at

producing crystals with the desired quality for specific applications. There are several

techniques used to grow crystals but each techniques aims at producing a crystal with such

quality good enough to be used for the desired application. Crystal growth may be achieved

using simple cheap techniques or complex and relatively expensive methods. The growth rate

and crystal sizes also vary with the method used. Crystals may be produced in the solid, liquid

or vapour phase and usually involves a controlled or tailored phase transformation. Based on

the phase transformation process, crystal growth techniques are classified as solid growth,

vapour growth, melt growth and solution growth.

Solid Growth - Solid-to-Solid phase transformation Liquid Growth - Liquid to Solid phase transformation Vapour Growth - Vapour to Solid phase transformation

Crystals will grow from a melt much more rapidly than the will grow from the vapour phase

or from solution. This is simply because the density of the material in the melt is comparable

to that in the crystal, so the atoms or molecules are essentially there already to grow the

crystal. For vapour and solution growth, the density of the atoms or molecules in the mother

phase is much lower, and the growth rate depends on the rate at which they arrive at thesurface of the crystal. For the commercial growth of crystals, the faster the crystals of

acceptable quality can be grown the better. This is also true for non-commercial growth of

experimental crystals. So melt growth is the preferred method. However there are various

reasons why many crystals cannot be grown from the melt as we shall see below.

Crystal growth involves two successive processes referred to as nucleation and growth

respectively. Nucleation is a process whereby tiny fragments called seeds crystals are

produced, this usually occurs when components of a solution start to precipitate out, forming

nuclei which attract more precipitate. The seed crystal then forms the base upon which the

growth occurs. Nucleation can occur spontaneously mostly due to changes in pressure and

temperature in which case it is referred to as homogeneous or it can be induced or aided in

which case it is referred to as heterogeneous. The two processes involved in crystal grow i.e.

nucleation and growth will be discussed in more detail.

Nucleation

For a crystal to grow, a seed capable of maintaining a stable condition in a solution, melt or

vapour phase has to be produced first. Nucleation requires the formation of a 3d nucleus.

In this experiment Copper (II) Sulphate Pentahydrate was grown using the temperature

reduction method. This method is a sub-group of the solution growth methods. As mentionedabove, crystal growth from solution is a slow process and the method is mostly used for

materials which cannot be grown from a melt. Some materials decompose or sublime below


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their melting point and cannot be growth from melts. This is true for Copper (II) Sulphate

Pentahydrate, therefore solution growth is the most appropriate method to use.

Aim of Experiment.

The aim of the experiment is to grow a single crystal of Copper (II) Sulphate Pentahydrate

from an aqueous solution by temperature reduction method.

Theory

Growth of crystals from low temperature aqueous solution is controlled by the temperature

and concentration of the solution. Materials, which possess high solubility and whose

solubility is temperature dependent, 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 thesolvents and the solubility of the solute. These include;

Temperature reduction method Isothermal evaporation method salting out

Copper (II) Sulphate Pentahydrate was grown by low temperature solution growth method. As

mentioned above, this method is applicable for materials with moderate to high solubility and

even more important is that the solubility should be highly temperature dependent. The

solubility of Copper (II) Sulphate Pentahydrate is very temperature dependent. At 0C the

solubility is about 250g/l of water and at 100C the solubility increases to more than 2000g/l

of water (see fig. 1).

Fig 1.The Solubility curve of Copper (II) SulphatePentahydrate in Water.


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This method is suitable to grow single crystals from starting materials which are either

unstable or undergo phase transformation under high temperatures. Copper (II) Sulphate

Pentahydrate as is a salt with a triclinic crystal structures, dehydrates at 150C and

decomposes at 650C. Other growth methods such as growth from melts, vapours or solid to

solid transformation will not be suitable to grow Copper (II) Sulphate Pentahydrate because

these other methods require much higher temperatures which may decompose or dehydrate

the material. The experiment was performed as follows;

Equipment

Fume hood, growth apparatus with control unit, bright lamp (e.g. cold-light lamp), drying

cabinet with temperature control, various beakers (3002000 ml) with appropriate

cover glasses (watch glasses), crystallizing dish, heating plate with magnetic rotation,

glass rod, thermometer (up to 80 C), filter paper with matching funnel, laboratorystand, clamps etc., nylon thread, latex gloves, lint-free paper towels, Teflon tweezers,

plastic tins for storage.

Chemical

1000g copper (II) sulphate pentahydrate, several litres of 18 Mcm H2O, detergents,

alcohol (e.g. isopropanol)

Procedure

The experiment was performed stepwise as follows:

Cleaning Preparation of growth apparatus Growth of seed crystals Preparation of saturated solution and the determination of saturation point. Growth of crystals End of growth, preparation of grown crystal, determination of growth rate End of Experiment.Cleaning

In order to avoid parasitic nucleation all the devices used in this experiment were freed from

all solid particles. This was achieved by thoroughly cleaning all the device parts as follows:

Flushing with soap water and rinsing with plenty of water Repeatedly rinsing with 18 Mcm H2O using a wash bottle Finally washing down with deionised water Dripping and drying in an oven at suitable temperaturesGrowth Apparatus Set-up and Preparation


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The outer vessel was filledwith water up to about 1-2 cm

below the aluminum ring. The

water level was tried to be

kept constant by replenishing

it from time to time.

The pump was started and thethermostat was set so the

water get a uniform

temperature of about 50C.

This is the growth

temperature.

The crystallizing vesselstogether with all the stirring

parts were thoroughly cleaned

initially with tab water then

with 18 Mcm H2O. The

vessels and the other parts

were then left to drain

The parts were rapidlyassembled to avoid dust from

getting into the vessel.

The growth apparatus used for this experiment is shown in the diagram below and it was

prepared a s follows:

Growth of Seed Crystals


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While the growth apparatus gets a uniform temperature a solution for the seed crystal was

prepared. The solution was prepared as follows:

30g of Copper (II) Sulphate Pentahydrate was mixed with 100ml of 18 Mcm H2O in a300ml cooking cup

The mixture was placed in a heating plate and heated to a temperature of about 50C andoccasional up to 60C to get all the Copper (II) Sulphate Pentahydrate into solution.

During the heating the solution was constantly stirred to help dissolution and keep a

uniform temperature throughout the solution.

The solution was then left to stay overnight at room temperature. The solution wascovered to prevent dust or other solid particles from getting inside as this might lead to

parasitic nucleation. The next day some seed crystals were formed.

The solution was filtered over the crystals into a crystallising dish The biggest of the seed crystal was selected to be used for the growth. A fishing line was tight around the seed crystal to enable it to be suspended in the growth

solution.

Preparation of Saturated solution and the determination of saturated point.


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The saturated solution was prepared in the following way:

A 3l flask , suction filter, and funnel were cleaned and heated (without the sealing cuffs)

to about 85C

A temperature of 50C was chosen as the growth temperature and the solubility Copper

(II) Pentahydrate at this temperature was determined using the solubility curves.

Based on this calculation, 0,657kg (per litre of water) of Copper (II) Pentahydrate is need

to make a saturated solution at 50C.

The mixture of the 0,657kg of Copper (II) pentahydrate and 1000ml of water was then

heated to about 60C on a heating plate with a Teflon stirrer. The cooking cup was

covered throughout the dissolution time.

A membrane pump was then used to filter the solution and the filtered solution was then

poured into the crystallising vessel in the growth apparatus.

The saturation point was determined by the streaking method using a crystal of lower quality.

The principle of the streaking method is shown schematically below.


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The test seed crystals and the attachment cord were clean with alcohol and briefly dipped in

deionised water to roughen the surface of the crystal. The crystal was then introduced into the

saturated solution and observed with a lamp from behind the growth apparatus. The

observation was to check for the three possible scenarios above. Alternatively the crystal was

left to stay in the saturated solution over night at the growth temperature. If the solution is not

saturated, the test crystal will dissolve, if the solution is over saturated, the test crystal will

grow and if the size does not change significantly, it means the solution has the right

saturation for this temperature. The test crystal did not show any significant change in size

after 24 hours and we assumed that the saturation point for the solution at the growth

temperature was reached.

Growth of Crystal

After being convinced that the saturation point of the growth solution is correct, the test

crystal was removed and replaced by the seed crystal. The seed crystal was also dipped in

deionised water to roughen the surface. Suspended on a nylon cord, the seed crystal was

slowly lowered into the saturated solution such that it was roughly in the middle of the vessel

with the saturated solution without touching the walls or bottom of the vessel.

After making sure that the seed crystals was in the desired position we proceeded with

temperature reduction. The switch was adjusted to the temperature reduction mode and the

temperature reducer was turned to position 1. The temperature was reduced at a 0,2

interval after every few days until the growth process was completed. At the end of the

growth period the growth apparatus was switched off and the crystal was left to stay in the

solution for more one night. This is to prevent thermal shock of the crystal. The crystal was

then removed and sprayed with a vanish coating to prevent it from absorbing moisture. The

crystal was measured and the growth rate was determined.


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Results and Discussions

The experiment lasted for four weeks in total. The first two days were used in the preparation

of the seed crystal, growth apparatus, growth solution and the determination of the saturationof the growth solution. The rest period was used for the growth. The diagrams below show

both the seed crystal and the grown crystal. The seed crystal has the dimension of 2,5cm by

3,5 cm and the grown crystal has the dimension of 4,5cm by 5,5cm.


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0 10 20 30

Growth [cm]

Time [days]

short axis

long axis

growth of copper real (autosaved)

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