Presented by Dhanashree. R. Kavhale... Thermal techniques of Analysis including Differential Scanning Colorimetry, Differential Thermal Analysis.

1. Thermal Techniques
Presented by
Dhanashree R. Kavhale
M. Pharm. (Pharmaceutical Chemistry) Sem- II
Department of Pharmaceutical Sciences
Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur - 440033

2. Contents
1. Introduction to thermal Techniques
2. Introduction of DSC
3. Principle
4. Instrumentation
5. Applications
6. Introduction of DTA
7. Principle
8. Instrumentation
9. Applications
10. References
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3. What are Thermal methods of analysis?
 A group of techniques in which change in physical property of a material is
measured as a function of temperature while the substance is subjected to a
controlled temperature programme.
 new materials are studied with respect to – composition, stability, chemical
reactions and dynamic properties.
 These methods also provide information about the structure, composition,
purity and the temperature phase change of a material.
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4. Classification of Thermal Techniques
Sr.No. Methods Properties measured
1 Differential scanning calorimetry (DSC) Temperature (∆T)
2 Differential thermal analysis (DTA) Enthalpy
3 Thermal gravimetric analysis (TGA) Reduced mass
4 Dynamic mechanical analysis (DMA) Deformation
5 Dielectric thermal analysis (DTA) Deformation
6 Evolved gas analysis (EGA) Gaseous decomposition
7 Thermal optical analysis (TOA) Optical properties
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5. Thermal Transitions
 Low molecular wt. material change their physical state as temperature
increases.
 At. Melting point change, visibly from crystal – liquid.
 At. B.P. liquid - vapour.
 Each true phase transition defined thermodynamically, by a marked change in
enthalpy, a marked change in enthalpy.
 These changes in enthalpy can only be determined with methods generally
employed to determine transition temperature.
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6. Differential Scanning
Calorimetry (DSC)
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7. Introduction of DSC
 A thermal analytical technique in which the difference in the amount of heat
required to increase the temperature of a sample and reference is measured as a
function of temperature.
 This technique is used to study what happens to polymers/samples upon heating.
 The differential scanning calorimeter does all of the above functions and heats
the sample with the linear temperature.
 Both the sample and reference are maintained at nearly the same temperature
through out the experiment in DSC.
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8. Principle
 It is a technique in which the energy necessary to establish a zero
temperature difference between the sample & reference material is
measured as a function of temperature.
 Here, sample & reference material are heated by separate heaters in such a
way that their temp are kept equal while these temp. are increased or
decreased linearly.
 During heating two types of reactions can be take place one is the
endothermic and the other is the exothermic.
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9. Exothermic reaction
 If sample released some amount
of heat during phase transition,
then reaction is said to be
exothermic.
 In exothermic reaction, less
energy needed to maintain zero
temp difference between sample
& reference.
 E.g. crystallization, degradation,
polymerization.
Endothermic reaction
 If sample absorbs some amount
of heat during phase transition
then reaction is said to be
endothermic.
 In endothermic reaction more
energy needed to maintain zero
temp difference between sample
& reference.
 E.g. Melting, boiling,
sublimation, vaporization.
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10. Heat flux DSC
 The sample and the reference cells are heated at a constant rate and
thermocouples are used to detect the temperature difference between sample
side and the reference side using single large mass furnace.
 The large single furnace which acts as an infinite heat sink to provide or
absorb heat from the sample.
 The dynamic sample chamber is the environment of the sample pan
compartments and the purge gas.
 Nitrogen is the most common gas, but alternate inert gas is helium or argon.
 When using an oxidative atmosphere air or oxygen are the gases of choice.
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11. Power compensation DSC
 It directly measures heat flow between sample side and reference side using two
separate, low mass furnaces.
 This individual furnaces use different amount of power to maintain a constant
change of temperature between sample and the reference.
 Platinum resistance thermometers track the temperature variations for the sample
and reference cells.
 Holes in the compartment lids allows the purge gas to enter and contact the
sample and reference.
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12. Instrumentation of DSC 12
Fig: Schematic representation of DSC

13. 1. Heat-flux DSC
 Sample Holder:
Platinum, aluminium, stainless steel.
 Sensors: Temperature Sensors
Usually thermocouples.
 Furnace: One block for both sample
and reference cells.
 Temperature: The temperature
difference between the sample and
reference is converted to differential
thermal power, which is supplied to
the heaters to maintain the
temperature of the sample and
reference at program value.
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14. 14
 Sample Holder:
Platinum, aluminium, stainless steel.
 Sensors: Pt resistance thermocouple
Separate sensors and heaters for the
sample and reference sample.
 Furnace: Separate blocks for sample
and reference cells.
 Temperature: Differential thermal
power is supplied to the heaters to
maintain the temperature of the
sample and reference at the program
level.
2. Power Compensated DSC

15. Reference material
 An inert material like alumina is generally used.
 An empty pan with lid is also used if the sample weight is small.
 With sample weight it is necessary to use reference material, because the
total weight of the sample and its container should be approximately the
same as the total weight of the reference and its containers.
 The reference material should be selected so that it posses similar thermal
characteristics to the sample.
 Most widely used reference material is alpha alumina Kieselguhr is another
reference material normally used when sample has a fibrous nature.
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16. Sampling
 Accurately-weigh samples (~3-20 mg)
 Small sample pans (0.1 mL) of inert or treated metals (AI, Pt, Ni,
etc.)Several pan configurations, e.g., open, pinhole, or hermetically-sealed
(airtight) pans.
 The same material and configuration should be used for the sample and the
reference.
 Material should completely cover the bottom of the pan to ensure good
thermal contact.
 Small sample masses and low heating rates increase resolution.
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17. 17
Fig: Representation of DSC curve

18. Factors affecting DSC curve
1. Instrumental factors
a. Furnace heating rate
b. Furnace atmosphere
Sample characteristics
a. Amount of sample
b. Nature of sample
c. Particle size
d. Heat of reaction
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19. Advantages
1. Rapidity of the determination.
2. Small sample masses.
3. Versatility Simplicity.
4. Applicable study many types of chemical reactions.
5. No of Need calibration over the entire temperature for DSC.
Disadvantages
1. Relative low accuracy
2. Not be used for overlapping reactions.
3. Difficulties in test cell preparation in avoiding evaporation of volatile
Solvents does not detect gas generation.
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20. Applications
 Purity determination of sample
directly
 Detection of polymorphism
 Quantification of polymorph
 Detection of meta stable polymorph
 Detection of isomerism
 Stability/compatibility studies
 Percentage crystallinity
determination
 Lyophilisation studies
 Finger printing
 Liquid crystals
 Oxidative stability
 Safety screening
 Drug Analysis
 General chemical analysis
 Food science
 Polymers
 Metals Protein analysis
 Choosing better solvent
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21. Differential Thermal
Analysis (DTA)
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22. Introduction of DTA
 Differential thermal analysis (DTA), is quantitative technique for
identifying or analyzing a chemical composition of substances by observing
the thermal behavior of a sample as it is heated.
 The technique is based on the fact that as a substance is heated, it undergoes
reactions and phase changes that involve absorption or emission of heat.
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23. Principle
 Technique in which the temperature difference between a substance and reference
material is measured as a function of temperature, while the substance and
reference are subjected to a controlled temperature programme.
 The Difference in temperature is called as Differential temp(∆t) is plotted against
temp. or a function of time.
 Physical changes usually result in Endothermic peak, whereas chemical reactions
those of an oxidative nature are exothermic.
 Endothermic reaction includes vaporization, sublimation.
 Exothermic reaction includes oxidation, polymerization, and catalytic reaction.
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24. Instrumentation
1. Furnace
2. Sample holder
3. Dc amplifier
4. Differential temperature detector
5. Furnace temperature programmer
6. Recorder
7. Control equipment
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25. 25
Fig: Schematic representation of instrumentation of DTA

26. 1.Furnace
 In DTA apparatus, one always prefers a tubular furnace.
 This is constructed with an appropriate material(9-11/30or ribbon) wound
on a refractory tube.
 These are fairly inexpensive.
 Generally, the choice of the resistance material as well that of refractory is
decided from the internal maximum temperature of operation and gaseous
environments.
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27. 2. Sample holders
 Both metallic as well as non-metallic are employed for the fabrication of sample
holders.
 Metallic materials generally include nickel, stainless steel, platinum and its alloys.
 Non-metallic material generally includes glass, vitreous silica or sintered alumina.
 Metallic holders give rise to sharp exotherms and flat endotherms.
 Non-metallic holders yield relatively sharp endotherms and flat exotherms.
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28. 3. DC Amplifier
 It is used for amplification of signals obtained from (T)c.
 It is gain and low noise circuit.
4. Differential temperature detector
 In order to control temperature, the three basic elements are required.
 These are sensor, control element and heater.
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29. Types of Differential temperature controller
On-off control
 In this device, if the sensor- signal
indicates the temperature has
become greater than the set point,
the heater is immediately cut off.
 Not used in DTA.
Proportional control
 In on-off controllers there occurs
fluctuations of temperature
around the set value.
 These can be minimized if the
heat input to the system is
progressively reduced as the
temperature approaches the
desired value.
 Such a controller that anticipates
the approach to the set value is
known as proportional controller.
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30. 5. Furnace temperature programmer/Sensors
 It provides smooth heating or cooling at a linear rate by changing the voltage
through heating component.
 Modern DTA instruments incorporate electronic temp controller in which the signal
from thermocouple in furnace is compared electrically against ref. potential which
can be programmed to corresponds to a variety of heating modes & heating rates.
6. Recorder
 In thermo-analytical studies, the signal obtained from the sensors can be recorded in
which the signal trace is produced on paper or film, heating stylus, electric writing
or optical beam.
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31.  There are two types of recording devices similar to the TGA.
1. Deflection type
2. Null-point type
7. Control Equipment
 For some type of samples the atmosphere must be controlled to suppress
and undesirable reaction such as oxidation by flowing an inert gas.
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32. Working of DTA
 The sample and reference standard are placed in the furnace on flat, highly
thermally conductive pans and the thermocouples are physically attached to
the pans directly under the sample.
 This procedure avoids or reduces any thermal lag resulting from the time
required for the heat to transfer to the sample and reference materials then to
the thermocouples.
 The thermocouple are connected in opposition.
 In a similar manner any change in state that involves a latent heat of transition
will cause the temperature of the sample to lag or lead that of the reference
standard and identify the change of state and the temperature at which it
occurred.
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33. Thermogram
 A differential thermogram consists of a record of the difference in sample and
reference temperature.
 (∆T)plotted as a function of time t, sample temperature(Ts) reference
temperature (Tr) or furnace temperature (Tf).
 In most of the cases physical changes give rise to endothermic curves whereas
chemical reaction gives rise to exothermic.
 Sharp endothermic - change in crystallinity or fusion.
 Broad endothermic - dehydration reaction.
 Exothermic - mostly oxidative reaction.
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34. 34
Fig: Thermogram

35. Advantages
1. Instruments can be used at
very high temperatures.
2. Instruments are highly
sensitive.
3. Characteristic transition or
reaction temperatures can be
accurately determined.
Limitations
1. ∆T determined by DTA is not so
accurate (2-3 C).
2. Small change in T cannot be
determined and quantified.
3. Due to heat variation between
sample and reference makes, it
less sensitive.
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36. Applications
1. Qualitative and Quantitative Identification of Minerals: detection of
any minerals in a sample.
2. Polymeric Materials: DTA useful for the characterization of polymeric
materials in the light of identification of thermo physical, thermo
chemical, thermo mechanical and thermo elastic changes or transitions.
3. Measurement of Crystalline: measurement of the mass fraction of
crystalline material.
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37. Continue..
4. Analysis of Biological Materials: DTA curves are used to date bone
remains or to study archaeological materials.
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38. Reference
 Instrumental methods of Chemical analysis by G.R. Chatwal.
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39. Thank you..
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