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Lecture 1 4-Nov-04 1

Thermal Analysis

SSK 4242

The Effect of Heat on Materials

Very important to human life why ???

The effect of heat on materials: change inmolecular and atomic vibration and ionic movement

Structural or shape change

Melting

Decomposition

Sintering

evaporation

a) CaCO3(s) CaO(s) + CO2(g)

b) NH4Cl(s) NH3(g) + HCl(g)

a) BaCl2.2H2O(s) BaCl2(s) + 2H2O(g)

b) CuSO4.5H2O(s) CuSO4(s) + 5H2O(g)

ii) Weaker inter-molecular force

i) Weaker intra-molecular force

2Ag(s) + O2 Ag2O(s)

4Al(s) + 3O2 2Al2O3(s)C(s) + O2(g) CO2(g)

PbS(s) + 3O2(g) 2PbO(s) + 2SO2(g)

a) CuO(s) + H2(g) Cu(s) + H2O(g)

b) SnO(s) + H2(g) Sn(s) + H2O(g)

Oxidation:

Reduction:


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Thermal Analysis

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Thermal Events

the formation of solid solution;

the formation of an eutectic mixture;

the formation of a new compound.

In case more than one solid materials involved

in the heat treatment, more thermal events will

take place leading to:

Formation of a new compound:

Fe2O3(s) + MgO(s)

MgFe2O4(s)

NaCl(s) + AgBr(s)

AgCl(s) + NaBr(s)

Double Decomposition:

Table 1.1 Summary of the

heat effect on materials

Table 1.2 The effect of

heat on solid materials
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Thermal Analysis

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Table 1.2 The effect of heat on solid materials (Haines, 1995)

Effect Conclusion Example

Colour effect

Charred, burned with

little residues

Organic, polymer Combustion of

papersBlackened with plenty

residues

Metal oxide is formed CuCO3CuO + CO2

Metal changed into

powder

Oxidation 2 Mg + O22 MgO


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Thermal Analysis

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Table 1.2 The effect of heat on solid materials (Haines, 1995) Contd.


Melting MaterialsMelt at low

temperature Covalent ? OrganicMelt at hightemperature Ionic salts NaCl

Sublime MaterialsWhite sublimation The solid is easilyevaporated

Ammonium salts

NH4Cl

Violet sublimation Iodine I2


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Thermal Analysis

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Released Vapours

(character ised by other

tests)Water droplets Hidrate CuSO

4.5H

2O

Oksigen Nitrate, chlorate 2KNO32KNO

2+ O

2

Nitrogen oxide (brown

fume)Nitrate 2AgNO3

2Ag + 2NO2 +O

2

Carbon dioxide Carbonate ZnCO3 ZnO+ CO

2


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Thermal Analysis

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Physical change

Maleable Plastic at greater than Tg

Expansion

(a) gradual

(b) abrupt

Normal expansion

Phase change

Swelling Some swelling materials Polyphosphate

Shrinkage Some strained polymers Fibres

No effect Oxide that is stable towards

heat or very low temperature

MgO, Al2O

3

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Thermal Analysis

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Heat Capacity

All materials have their own heat capacities

an ability for the materials to absorb and keep the heat energy

Mechanisms of retaining heat energy:

a) Solid materialsThe heat energy is kept via atomic vibration about

a min position around the atom in the lattice

b) Metallic materials

c) Liquid materials

The heat energy is also kept via the electronic

movement of the metal

The heat energy is kept via the rotational

movement of the atoms, therefore liquids

generally have greater heat capacity than the

solid materials.


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Thermal Analysis

SSK 4242Heat Capacity (Cp)

the amount of heat that is required to raise the temperature of a body by 1 Kelvin

The absorbed heat is stored as enthalpy Cp is also a measure of the amount of enthalpy change when the body

temperature is raised by 1 Kelvin

Cp = H / T

International Confederation for Thermal Analysis and Calorimetry (ICTAC)

Thermal analysis is defined as a group of techniqueswhere the properties of samples are monitored versus

time or temperature while the samples temperature is

controlled under certain atmosphere

Definition of Thermal Analysis:

Table 1.3 Parameters and

techniques in the

measurement of heat effect
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Thermal Analysis

SSK 4242Heat Capacity (Cp)

the amount of heat that is required to raise the temperature of a body by 1 Kelvin

The absorbed heat is stored as enthalpy Cp is also a measure of the amount of enthalpy change when the body

temperature is raised by 1 Kelvin

Cp = H / T

International Confederation for Thermal Analysis and Calorimetry (ICTAC)

Thermal analysis is defined as a group of techniqueswhere the properties of samples are monitored versus

time or temperature while the samples temperature is

controlled under certain atmosphere

Definition of Thermal Analysis:

Table 1.3 Parameters and

techniques in the

measurement of heat effect
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Thermal Analysis

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Parameter Measuring Technique Abbreviation

Mass change with temperature Termogravimetry TGMass change with temperature change Derivative Termogravimetry DTG

Sample temperature change with

temperature

Differential Thermal Analysis DTA

Enthalpy change with temperature Differential Scanning Calorimetry DSC

Dimensional change with temperature Termodilatometry

Change in mechanical properties with

temperature

Thermomechanometry or

Dynamic Mechanical Analysis

TMADMA

Change in optical properties with

temperature

Thermoptometry/

thermomicroscopy

Change in magnetic properties with

temperatureThermomagnetometry

Change in electrical properties with

temperature

Thermoelectrometry

Table 1.3 The parameters and techniques in the measurement of heat effect

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Thermal Analysis

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Temperature Control Programme

a) Heating or cooling at a constantly changing temperature

b) Heating at a constant temperature

c) Combination of (a) and (b) above.

Sample

The material that is placed in the instrument at the beginning of

the experiment

The reaction products

Thermogram

The thermal analysis curve

The experimental data in a graphic form


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Thermal Analysis

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Differential Thermal techniques:

These Involve measurement of the differential properties/values

between samples and the reference materials

Derivative Thermal techniques:

These involve measurement or calculation of mathematical

derivation versus time

Example: the differential thermal analysis (DTA) where the measured

parameter is the difference between the sample temperature

and the reference temperature

Example: the derivative thermogravimetry (DTG) that involves

measurement of the rate of mass loss (dm/dt) plotted versus

temperature, T.


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Thermal Analysis

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Measurement of Heat Effect

Sample

Reagent (Heat)

Signal

Sample

Signal

generatingunit

Heat

Signal

Information about the sample


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Thermal Analysis

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m

T

m / T

T

T

T

H / T

T

Thermal Analysis Techniques, the Measured

Parameters and the Thermograms

a) Thermogravimetry (TG) b) Derivative Thermogravimetry (DTG)

c) Differential Thermal analysis (DTA) d) Differential Scanning Calorimetry (DSC)

Mass loss

The rate of mass change versus

the temperature change

The temperature difference between the

sample and the reference versus the

temperature change Heat flow versus the

temperature change


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Thermal Analysis

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Conditions for Heat Effect Measurement

1. Measurement of the physical properties and the

sample temperature should be made

continuously,

2. Measurement and recording of both parameters

should be made automatically,

3. The temperature change of the sample(increased or reduced) takes place at a constant

rate.


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Thermal Analysis

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Asbestos Glass Catalysts

Liquid crystal Ceramics Metals and steels

Clay Minerals Explosives

Organic materials Inorganic chemicals Fats, oils and waxes

Organometallics Fertilizers Pharmaceuticals

Fuels Plastics Rubber

Textiles Foods Plant materials

Application of Thermal Analysis

Some examples of materials that can be studied by Thermal Analysis Methods

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