THE EXPERIMENTAL PARAMETERS USED IN DSC INCLUDING SAMPLE PREPARATION , EXPERIMENTAL CONDITIONS, CALIBRATION OF APPARATUS, INSTRUMENTS, HEATING RATES AND TEMPERATURES, COOLING RATES,RESOLUTION, ALSO SOURCE OF ERRORS.

1. EXPERIMENT PARAMETERS OF
DIFFERENTIAL SCANNING
CALORIMETRY (DSC)
 Sample preparation
 Experimental conditions
 Calibration
 Heating rates
 Cooling rates
 Resolution
 Source of errors

2. Sample preparation
 The ideal DSC sample would be a thin circular disk, of high
thermal conductivity, that did not interact with the DSC cell
so that it could be placed directly inside without the need to
encapsulated the material in a sample pan.
 This criteria meet the need for minimize thermal gradients
within the sample and reducing the thermal resistance of the
DSC.

3. Sample form :
1 Powders : Ideally these should be free flowing
and, if necessary, of a consistent particle size
distribution.
• If material contains “lumps” it may be necessary
to pass a portion of the sample through two
sieves (50 and 100um) and runs the portion
collected in between.
• The presence of agglomerates or other lumps
within a sample can lead to shoulders appearing
on the DSC heat flow curve during transitions.

4. 2 Liquids : Low viscous liquids can be transferred to
the hermetic DSC pan using a Pasteur pipette or
similar apparatus.
• Dipping one end of an opened paper clip into
viscous liquids and then placing it onto the base of
the sample pan may transfer higher viscosity
samples.
3 Cream and Emulsion: Poor reproducibility can
result if the sample is not homogenous.
• If possible, stir or shake the container prior to
sampling.
• Use similar technique to those describe for
handling liquid samples.

5.  Organic material can also exist in crystalline and amorphous
form. The first transition can be observed as an endothermic
shift in the baseline. This is the glass transition temperature.
As the temperature increases an exothermic peak may be
observed if the sample can oriented into a more crystalline
form. Finally, any crystalline material present may melt or
(as in this case) melts and decompose at higher temperature.

6. Sample size: As the sample mass is increase
so does the time increase that is required for
that sample to melts.
 When a material is melting, its temperature
stays constant.
 As the sample mass increases there is an
increase in the thermal gradient across the
sample. This leads to a decrease in the slope
on the leading edges of the heat flow data
obtained during melting.
 The size of sample is 0.5mg to 10mg

7.  Effect of changing sample mass on the
transition measure by DSC.
SAMPLE
SIZE
SENSITIVIT
Y
RESOLUTI
ON
ONSET
TEMPERAT
URE
PEAK
MAXIMUM
TEMPERAT
URE
Increase Increase Decrease Constant Increase
Decrease Decrease Increase constant Decrease

8. Sample Pan :There is a wide range of sample
pans available, designed to meet general and
specific sample and application needs.
 Once the sample and reference pan have been
introduced into the DSC, it is important to
wait for thermal equilibrium to be re-
established (stable heat flow signal) before
starting the experiment.
 The types of pan available can be divided into
three general types: general pan, hermetic pan
and high pressure pan.

9. 1 General pan : These are usually used for most powder
and solid samples, and come in two parts pan and lid.
 The pan is sealed by pressing the lid, using a dedicated
sealing press.
 Available in various material, aluminium is typically
used for pharmaceutical materials.
 If the sample react with aluminium then either anodized
aluminum, platinum or gold pans may be used.
 Consequently, all pans should be cleaned with solvent
(nonchlorinated) and stored in a desiccator prior to use.
If all these pans are used without cleaning, the oil can
leads to spurious events appearing on the DSC trace.

10. 2 Hermetic pans : Hermetic pans can be sealed
without the need to place any stress or pressure
upon the sample. Again they come in two parts
pan and lid.
 Slightly thicker aluminum is used in the
manufacturing of hermetic pans to ensure that a
good gas seal is obtained.
 If the inert atmosphere is needed around the
sample during the DSC experiment, then the pans
should be sealed in glove box that is purged with
nitrogen.
 Hermetic pans are also ideal for running liquids,
emulsions, and creams.

11.  In sealed hermetic pan the maximum pressure for
aluminum pan is ~300kpa and maximum pressure
for gold ~600kpa and maximum temperature 600
degree Celsius.
 Typical volume is ~40ul
 Sealed hermetic pan with inverted lid use unless a
large sample size is required.
3 High pressure pans : In high pressure pan the
pressure is higher than ~300kpa, material other
than aluminum, and with different sealing system
are used.
 A variety of pan types exist with specific
temperature, pressure and volume restriction.

12. A. O-Ring sealed pans : By using stainless steel as
the pan material and o-ring as the sealing
mechanism, these pan can withstand pressure
up to 3MPa. The thermal lag of these pans is
much higher than hermetic pan due to the use of
thick stainless steel as the pan material.
Maximum temperature is ~250*C and typical
volume ~100ul.
B. Washer sealed pan :By increasing wall
thickness and using a metal washer as a soft
metal seal, these pan can hold pressure 10MPa.
And maximum temperature is ~300*C and
typical volume ~70ul.

13. C. Glass Ampoule pans : Glass ampoule are used
for samples that might react with metallic
crucible or for assessing stability and reactivity.
Maximum pressure is ~20MPa and temperature
is ~600*C and typical volume ~50ul. The sealed
glass ampoule is then either placed directly in
the DSC or placed inside a metals carrier to
ensure good heat transfer to the sample.

14. Experimental conditions
1. Analytical balance: The analytical balance is
used to weigh out the sample is often the
limiting factors in regard to the accuracy of the
heat flow signals produced by the DSC.
 The balance should be checked and calibrated
daily against a known traceable reference
weight.
 A 5 digit balance should be consider as
minimum requirement when weighing samples
in the 10 to 20mg range, 6 digit balance for 1 to
10mg range and 7 digit balance for sample less
than 1mg.

15. 2. Purge gas: Most DSC experiment are carried out
in an inert atmosphere, usually Nitrogen.
 Helium which has a higher thermal conductivity,
can be used if the thermal resistance of the DSC
needs to be reduced.
 A drawback to using helium over nitrogen as
purge gas is that it takes considerably longer for
the DSC system to reach equilibrium and stabilize
after the cell has opened to air. This is because the
difference in thermal conductivity between helium
and air is much greater than the difference in
thermal conductivity between nitrogen and air.

16. 3. Purge flow : A constant purge of gas through the DSC
ensure that any volatile products evolved during the
DSC experiment are swept away from the measuring
sensor.
 A change in the flow rate of the gas used to purge the
DSC can have several effect.
 First, it is possible that it will change the temperature
and enthalpy calibration.
 Second, for experiment where a volatile substance is
evolved from the sample when its heated, the DSC peak
shape will be affected by the speed at which the volatile
substance is removed.
 This effect may be minimized by the use of two-stage
cylinder regulator or ideally the use of calibrated mass
flow controllers.

17. Calibration
1. Temperature calibration : The DSC experiment where
the sample is heated, the sample and its surroundings
are not in thermal equilibrium. The sample temperature
will be slightly lower than furnace temperature.
 Temperature calibration requires that traceable
standards, with known transitions temperature, be runs
under exactly the same conditions as those to be used
when running samples.
 It is also common to see an operator calibrate with two
materials indium and some other higher melting point
metals such as lead (327.5*C) or tin (231.93*C) then
analyzed the sample with transitions in the ambient to
100*C temperature range.

18. 2. Enthalpy calibration: Few materials exist that
have accurately known enthalpies and that are
also available with traceable certifications.
 The material can be used, in a single
experiment, to calibrate the DSC for both
abscissa and ordinate.
 The assumption is that a single enthalpy
calibration is acceptable for the entire
temperature scale.

19. Heating rates
 The several points can be observed as the heating rate increased: 1. The
baseline curves are increasingly offset.
2. The height magnitude and width of the melting peak increases.
3. The melting transitions is observed at higher temperature.
 As the heating rate increased, the width of the melting transition increases,
so resolution is decreases.
 The peak height increases, so the detection limit (the ability to differentiate
a transition above instrumental noise) is increases.

20. Effect that changing the heating rate
has transitions measured by DSC
HEATING
RATE
RESOLUTIO
N
SENSITIVIT
Y
EXPERIMEN
TAL TIME
Increases Decreases increases Decreases
Decreases increases Decreases Increases

21. Cooling rates
 Cooling is often an under-appreciated property of DSC.
 In controlled cooling a specific temperature change per
minute is specified as a rate between 0.1*C/min to
500*C/min and should be maintained through out the
experiment.
 In ballistic cooling where the sample is cooled as fast as
possible. The ballistic cooling rate of 400*C/min.
 For improve cooling times and subambient temperature
tests, various cooling options such as forced air, intracooler
or liquid nitrogen cooling system are available.

22. Resolution
 One of the most important performance
characteristic of DSC instrument is its Resolution.
 The resolution of a DSC is also a function of the
given experimental conditions including:
• Purge gas
• Sample mass
• Heating rate
 Enhance resolution can be obtained using a
helium rather than a nitrogen, air or oxygen
purge, due to the significantly higher thermal
conductivity of helium.

23.  Lower sample masses can provide improve
resolution over larger masses.
 Slow heating rate will yield significantly better
resolution than faster heating rates.

24. Source of errors
1. Environmental error
2. Instrumental error
3. Sample characteristic
A. Environmental error: The DSC technique is
more sensitive to the gaseous environment
around the sample the TG.
• In DSC studies two types of gaseous
atmosphere are used: (a) A static atmosphere
(b) A dynamic gaseous atmosphere.

25.  A static gaseous atmosphere is difficult to
reproduce because the atmosphere surrounding the
sample is changing in concentration chemically
due to evolved gases and physically due to
convection currents.
 A dynamic atmosphere where the gases are swept
past the sample in a controlled way are reliable
and reproducible. The sweep gases can be either
inert or reactive.

26. B. Instrumental error: The geometry and the
material used in the fabrication of the sample
holder affects the resolution, shape and size of
the DSC peak.
 In furnace heating rate increases the resolution
decreases and experiment time decreases. If the
winding used in furnace is not uniform, the base
line is changed.
 The heating rate has a great influence on the
DSC curve.

27. C. Sample characteristic: Particle size alters the peak
area. This decrease with increasing particle size.
 Particle size also influence the peak temperature.
Generally with increase in particle size, the peak
temperature is shifted to higher values.
 The shape of the sample has little effect on the
quantitative aspects of DSC but has more effect on
qualitative aspects.
 About 0.5 to 10mg is usually sufficient. Smaller
sample enable faster scanning, give better shape peaks
with good resolution and provide better contact with
the gaseous environment.

28. ADVANTAGES AND DISADVANTAGES
Advantages: Instruments can be used at very high
temperature.
 Instrument are highly sensitive.
 Flexibility in sample volume or sample form.
 Characteristic transition or reaction temperature can
be determine.
 High resolution obtained.
 High sensitivity.
 Stability of the material.
 Small amount of material is needed.

29. Disadvantages: Interpretation of results is often
difficult.
 Quantitative analysis of the individual processes
is impossible.
 Cannot optimize both sensitivity and resolution in
a single experiment.
 Very sensitive to any changes.

30. Applications of Differential
scanning calorimetry Identification of substance :- The DSC curve for
two substance is not identical. Therefore serve as
finger prints for various substances.
 Identification of products:- When substance reacts
with another substance, the products is identified
by their specific DSC curves
 Quantitative Analysis:- The area of DSC peak is
proportional to the total heat of reaction and hence
to the weight of the sample. Therefore the
quantitative analysis is possible with the help of
standards curves of peak area vs weight.

31.  Quality control:- DSC technique has been widely
used for the quality control of a large number of
substance like cement, glass, soil, textiles,
catalysts, explosives, resins etc.
 Determine crystalline to amorphous transition
temperature in polymers and plastic and the
energy associate with the transitions.
 Measure heat capacity in a range of temperature.
 Determine the thermal stability of a material.
 Determine the reaction kinetics of a materials.
 Metal alloy melting temperature and heat of
fusion.

32.  Determination the melting behaviour of complex
organic material, both temperature and enthalpies
of melting can be used to determine purity of a
material.
 Metal magnetic or structure transitions
temperature and heat of transformations.
 Determine crystallization and melting
temperature and phase transitions energies for
inorganic compounds.

33. Thank you