The presentation gives a detailed description of Differential Thermal Analysis and Differential Scanning Calorimetry.

1. Ms. Neha S. Raut
M.Pharm
DIFFERENTIAL THERMAL
ANALYSIS
&
DIFFERENTIAL SCANNING
CALORIMETRY
Smt. Kishoritai Bhoyar College of Pharmacy, Kamptee

2. INTRODUCTION
Differential thermal analysis is a technique
measuring the difference in temperature between a
sample and reference (a thermally inert material) as a
function of the time or the temperature, when they
undergo temperature scanning in a controlled
atmosphere. The DTA method enables any
transformation to be detected for all the categories of
materials.

3. Here,
Differential temperature ∆T (Temperature difference between
sample temperature Ts & reference temperature Tr.)
∆T = Ts – Tr
Reference temperature Tr or furnace temperature Tf & ∆T is
plotted as a function of time.
DTA
curve

4. From the graph,
▪ Sharp exothermic peaks give the ideas of changes in
crystallity or fusion process.
▪ Chemical reaction (Oxidative reaction) shows Exothermic
curve.
▪ Broad endothermic peaks gives signifying dehydration
reaction.
▪ Physical changes shows Endothermic curve.
▪ DTA curve would be parallel to the temperature (or time)
axis till the sample undergo any physical or chemical
changes.

5. INSTRUMENTATION
Component of a DTA apparatus
 Furnace
 Sample Holder
 DC Amplifier
 Differential Temperature Detector
 Furnace Temperature Programmer
 Recorder
 Control Equipment

6. Diagram of DTA apparatus

7. SAMPLE HOLDER
1.Material
Criteria for selection of material
▪ Cost
▪ Ease of fabrication
▪ Inertness towards the reactants & product in the
temperature range.
Types of material
➢ Metallic material:
High thermal conductivity
Ex. Nickel, Stainless steel (up to 1000oC),
Platinum and its alloys.
Give sharp exotherm and flat endotherm.

8. ➢ Non metallic material:
Low thermal conductivity
Ex. Glass,Vitrous silica or sintered alumina.
Give flat exotherm and sharp endotherm.
Generally platinum is used.
Disadvantage: Catalyses many reactions.
2. Geometry
Ideal geometry around thermocouple junction is
spherical but show problem in fabricaion.Hence
cylindrical shape generally used.

9.  Types of sample holders
Sample holder with dimples
in which thermocouple
junctions are inserted,dimples
known as thermocouple well.
To investigate several
samples simultaneously
blocks with symmetrically
located multiple
compartments have been
designed.

10. The reference
temperature may be
measured either at the
center of reference or
sample using
respective arm of the
differential
thermocouple in (A)
By a separate
thermocouple in block
(B)
(A)
(B)

11.  Polyp late sample holder and wire gauge
crucibles are used for a good exchange of gases
with the enveloping environment, where the solid
gas reactions are influenced by the partial pressure
of the gaseous reactant or product.

12. FURNACE
The choice of furnace geometry and heating
element mainly depend upon the length of uniform
temperature zone desired.
The furnace which cover the range
from -1900C to 28000C
Heated by
A resistance element: nichrome, platinum ,rhodium
globar, molybdenum and tungsten.
IR Radiation
High frequency RF oscillator
By a coil of tubing through which a heated or
cooled liquid or gas is circulated.
Always prefer tubular furnace.

13.  A relation between the power demand P in watts, furnace
dimension and temperature for a cylindrical tubular
furnace.
P = 2.729Km (T1 – T2) l
log d2 / d1
Where, l = length in cm
Km= Average thermal conductivity coefficient of
the insulation(Watt/cm2. K)
d1=Diameter of the heater coil wound on the
ceramic
d2=Diameter of furnace shell
T1&T2=Temperature of heating element and
surface temperature of the furnace shell

14. TEMPERATURE CONTROLLER & RECORDER
Temperature control
To control temperature, three basic elements
are required.
➢ Sensor
➢ Control element
➢ Heater
Control element governs the rate of heat input
match with heat loss from the system.

15. Two methods for controlling temperature:
On-Off control: In this device, if the sensor
signal indicates that the temperature increases
than the set point, then the heater immediately
cut off.
Not use in DTA(Reason-Electrical interference
affect measurement of signals).
Proportional control: The heat input to the
system is progressively reduced as the
temperature approaches to the desired value.
such controller that anticipates to set value is
known as “proportional controller”

16. Temperature Programmer
To produce desired rate of heating, cooling and to
maintain the constant temperature at any desired value,
thermal apparatus require time dependent temperature
cycling of the furnace.
To achieve this, a temperature programmer which
transmits a certain time based instruction to control unit.
Recorder
The signals obtained from the sensor recorded. Signal
trace is produce on paper or film ,heating stylus,
electrical writing or optical beam.
▪ Deflection type
▪ Null type

17. I) Deflection Balances:-
a) Beam type:- In this type of
balance, the conversion of
beam deflection about the
fulcrum into suitably
identified weight change
curve by photographic
recorded trace.
b) Helical or spring balance:- In
this type, the elongation or
contraction of spring with
weight change can be
determined.

18. c)Cantilever type:- In this one
of the beam is fixed & other
end on which sample is to
be placed is free to undergo
deflection.
d)Torsion type:- Beam is
attached to the taut wire
which act as fulcrum. The
wire is finally fixed at both
the end so that the
deflection of beam are
proportional to weight
change & tortional strain
of wire.

19. II)Null Point Balance:-
▪ In this type there is sensor to detect deviation of the balance
beam from the null position.
▪ The restoring force either electrical or mechanical weight
loading is applied to restore its null position from the
horizontal norm.
▪ The force is directly proportional to weight change.

20. THERMOCOUPLE (TEMPERATURE SENSOR)
Selection criteria :
 Temperature interval
 Thermoelectric coefficient
 Chemical capability with sample
 Chemical gaseous environment used and
reproducibility of EMF Vs. Temperature curve
as a function of thermal cycling.
 Availability and cost

21. THERMOCOUPLE TEMPERATURE
Copper couple Up to 3000C
Cromel - alumel
couple
Up to 10000C
Platinum couple Up to 15000C
Tungsten & Rhenium
in inert gas
or vacuum
Up to 21000C
(not for general use)

22. FACTORS AFFECTING ON DTA CURVE:
Environmental :-
The DTA technique is more sensitive to gases around sample than TG.
Reaction of gases with sample may give extra peaks in curve (i.e.
oxygen in air gives oxidation reaction producing exothermic peaks).
So to control such reaction DTA studies used two type of gaseous
atmosphere.
▪Static
▪Dynamic
▪ Static:-it is difficult to reproduce because atmosphere surrounding the
sample changing in the concentration chemically due to evolved gases
and physically due to convention current therefore the studies in the
static gaseous environment is imprecise.
▪ Dynamic:- Easy to reproduced. gases are swept pass the sample at
controlled way are reliable and reproducible. This swept gases are
either inert or reactive.

23. Instrumental:-
a)Sample holder:- Geometry & the material used in the fabrication of
the sample affects the resolution , shape, size of the DTA peaks.
❑ If sample holder made up of ,
1. High thermal conductivity material (metal)- sharp exothermic but
relatively flat endothermic peak .
2. Poor thermal conductivity material (ceramic)-the reveres will
happen.
For better resolution the size of the holder and amount of sample
should be as small as possible.
b)Differential temperature sensing devices:- Generally wires are
used.
1. If thick wire is used:- more distortion of peak height & peak
temperature.
2. If thinner:- lesser distortion in peak height and peak temperature.

24. c) Furnace characteristics:-
1. Type of winding directly affects the DTA curve. If the
winding used in furnace is not uniform, the base line
is changed. This type of effect is generally seen in
hand wound furnaces.
i) Grooved muffled cores furnace is used because it
insure uniform winding.
ii) Biflar winding also used because it minimize the
magnetic pick-up encountered with on –off controller.
d) Temperature programmer controller:-
Switching on –off type controller are not used because
it produces noise at a particular temperature range
i.e. a. bow 700oc.
Motor driver is used.

25. e) Thermal Regime:-
➢ Heating rate influence the DTA curve.
➢ Higher the heating rates ,higher the peak temperature&
sharper the peak intensity.
Generally heating rate of 100 to 200 per minute are employed.
f) Recorder:-
➢ Type, span, chart-speed and pen response ,sensitivity of
recorder affect the DTA curve.
➢ Span is not proper then necessary to preamplify the signals.
➢ If sensitivity is not properly selected, weaker signals would
not be recorded whereas stronger signals might be
damping.
➢ If faster chart-speeds used , DTA curve gets flattened.

26.  Sample characteristics:-
a) physical:-
▪ one assumption that heat capacity remain constant with the
progress of reaction but it changes with progress of reaction.
▪ To maintain the heat capacity nearly constant , the usual
sample is mixed with an excess amount of an inert material.
But it create some problems.
▪ Partial size affects the peak area , it deceases with increasing
particle size.
▪ Partial size affects the peak temperature. Increase particle size
the peak temperature is shifted to higher value.

27. ▪ Weight of sample also affect the peak intensity &
temperature. Both this increases with increasing
weight.
▪ To minimize all this problems sample is mixed with
a diluents.
b) Chemical :-
➢ The chemical reactivity of sample, sample holder,
thermocouple material, the ambient gaseous environment and
added diluents alters the DTA curve(peaks) .
➢ Select this material inert chemically as possible.

28. APPLICATION
1. Physical chemistry
a. Heat of Reaction:
Borchardt & Daniels concluded that the peak area A in
DTA is always a linear function of the heat of reaction,
∆H, when the rate of heat of production or consumption is
a function only of time.
The heat of reaction per mole is given by
∆H =KA/N0
Where, N0 = Initial no. of moles
K= Constant (Calibration coefficient)

29. b. Specific heat
DTA used to determine the specific heat of substance like
naphthalene.
The Cp was determined by following formula:
KK| (b – a)
Cp =
d ms dt
where,
K & K| = Constant (determined from
calibration curve of standard substance)
d = Density of sample
ms = Mass of sample
dt = The temperature interval over which
Cp is measured.

30. c. Thermal diffusivity
To determine thermal diffusivities by measuring
the temperature difference ,∆T,
between the center and surface of the sample, heated
at uniform rate.
The difference in temperature was measured by
using differential thermocouple.
ß r2
D =
6 ∆Ts
where,
r = Radius of spherical sample cavity
ß = Heating state

31. 2. Analytical Chemistry
a. Polymer analysis
Analysis of a polymer shows several features due to physical and
chemical changes, including:
 Glass transition: Transition from disordered solid to liquid,
glassy, amorphous polymer becomes flexible, H = 0, but change in Cp.
 Crystallization of amorphous polymer into microcrystal is
exothermic. Disordered to ordered transition.
 Melting of polymer crystal. Ordered to disordered transition
Oxidation peak would be absent in N2 atmosphere

32. 
T
b. To fingerprint substances
DTA of (a) butter and (b) margarine
temp →
a
b
c. To determine M.Pt., B.Pt., decomposition temperatures of
organic compounds
DTA of benzoic acid
A ambient pressure;
B 200 lb in-2 pressure

33. 3. Quality control
DTA technique used for quality control of substance like
cement, glass, oil, catalysts, textile, explosives, resins ,
etc.
 Characterization of limestone used in Portland cement
 To control amount of magnesium carbonate in cement
 To establish slag content present in a mixture of
Portland cement & blast furnace slag
 Characterization of gypsum plasters & corcidolite.

34. 4.INORGANIC CHEMISTRY
 To study the thermal stability of large number of
inorganic compound and complexes.
 To study oxalates, metal amine complexes,
carbonates and oxides.
 To study the oxides of uranium and plutonium.
Uranium dioxide powder with good sintering
qualities has been observed to give well defined
and well separated DTA peaks.

35.  Advantages:
• instruments can be used at very high
temperatures
• instruments are highly sensitive
• flexibility in crucible volume/form
• characteristic transition or reaction
temperatures can be accurately determined
 Disadvantages:
• uncertainty of heats of fusion, transition, or
reaction estimations is 20-50%
• less satisfactory than DSC with regard to
resolution of thermal traces and qualitative
data.

36. INTRODUCTION
Differential scanning calorimetric is a technique
determining the variation in the heat flow given out
or taken in by a sample as a function of temperature
or time.
The DSC curve is recorded with the chart
abscissa indicating the transition temperature . The
area of peak measures the total energy transfer to or
from the sample.

37. INSTRUMENTATION
➢ A typical DSC consists of two sealed pans: a sample
pan and a reference pan(empty). These pans are often
covered by or composed of aluminum, which acts as a
radiation shield. The two pans are heated, or cooled,
uniformly while the heat flow difference between the
two is monitored.
➢ This can be done at a constant temperature
(isothermally), but is more commonly done by
changing the temperature at a constant rate, a mode of
operation also called temperature scanning.
➢ The instrument detects differences in the heat flow
between the sample and reference.

38. ➢ This information is sent to an output device, most
often a computer, resulting in a plot of the differential
heat flow between the reference and sample cell as a
function of temperature. the differential heat flow is
calculated by subtracting the sample heat flow from
the reference heat flow.
➢ The sample is generally placed in an aluminum sample
pan. The reference consists of a matched empty
aluminum sample pan that is placed in the reference
cell of the instrument. The sample pans are designed to
have a very high thermal conductivity.
➢ Sample sizes generally range from 0.1 to 100 mg. This
also allows experiments to be performed under
variable pressures and atmospheres.

39. TYPES OF DSC INSTRUMENT
1.Heat Flux DSC:-
sample
pan
inert gas
vacuum
heating
coil
reference
pan
thermocouples
chromel wafer
constantan
chromel/calomel
wires
crimped Al pans (<500 o C)

40. ▪ sample holder : sample and reference are connected by
a low-resistance heat flow path
Al or Pt pans placed on constantan disc
▪ Sensors: Chromel®-constantan area thermocouples
(differential heat flow)
Chromel®-alumel thermocouples (sample temperature)
▪ Furnace: One block for both sample and reference cells
▪ temperature controller: temperature difference between the
sample and reference is converted to differential thermal
power, did/dot, which is supplied to the heaters to maintain
the temperature of the sample and reference at the program
value

41. 2.Power Compensated DSC
sample
pan
T = 0
inert gas
vacuum
inert gas
vacuum
individual
heaters
controller P
reference
pan
thermocouple

42.  Sample holder:
Al or Pt pans
 Sensors:
Pt resistance thermocouples separate sensors
and heaters for the sample and reference
 Furnace:
separate blocks for sample and reference
cells
 Temperature controller:
differential thermal power is supplied to the
heaters to maintain the temperature of the
sample and reference at the program value

43. FACTORS AFFECTING DSC CURVES
a. Sample shape:
The shape of sample has little effect on quantitative
aspect but more effect on quality aspect.
Sample in the form of a disc film or powder spread
on the pan are preferred.

44. b. Sample size
0.5 to 10mg usually sufficient.
Smaller sample:
▪ Faster scanning
▪ Better shaped peak with good resolution
▪ Provide greater contact with the gaseous environment
Larger sample
 Smaller heat of transitions may be measured with greater
precision.
c. Power supply
;
Variation of power supply to
sample & reference
DSC curve

45. APPLICATION
DSC can be used for all application of conventional DTA.
Use in industry for small size of sample
To detect phase changes and decompositions.
Ex.- DTA & DSC of CuSO4 .5H2O
DTA DSC

46. To study the oxidative stability of samples generally
requires an airtight sample chamber. Usually, such tests are
done isothermally (at constant temperature) by changing
the atmosphere of the sample. First, the sample is brought
to the desired test temperature under an inert atmosphere,
usually nitrogen. Then, oxygen is added to the system. Any
oxidation that occurs is observed as a deviation in the
baseline. Such analyses can be used to determine the
stability and optimum storage conditions for a compound.
Consequently, less pure compounds will exhibit a
broadened melting peak that begin sat lower temperature
than a pure compound.

47. In the pharmaceutical industry it is necessary to
have well-characterized drug compounds in order to
define processing parameters. For instance, if it is
necessary to deliver a drug in the amorphous form, it is
desirable to process the drug at temperatures below
those at which crystallization can occur.
In food science research, DSC is used in conjunction
with other thermal analytical techniques to determine
water dynamics. Changes in water distribution may
be correlated with changes in texture. Similar to
material science studies, the effects of curing on
confectionery products can also be analyzed.

48. In last few years this technology has been involved
in metallic material study. It is known that it is
possible to use DSC to find solids and liquids
temperature of a metal alloy, but the widest
application is, by now, the study of precipitations,
Gainer Preston zones, phase transitions,
dislocations movement, grain growth etc.
For the polymer chemist, DSC is a handy tool for
studying curing processes, which allows the fine
tuning of polymer properties. The cross-linking of
polymer molecules that occurs in the curing process
is exothermic, resulting in a positive peak in the DSC
curve that usually appears soon after the glass
transition.

49. DSC curves may also be used to evaluate drug and
polymer purities. This is possible because the
temperature range over which a mixture of compounds
melts is dependent on their relative amounts. This effect
is due to a phenomenon known as freezing point
depression, which occurs when a foreign solute is added
to a solution.
Used in the study of liquid crystals. As matter transitions
between solid and liquid it often goes through a third state,
which displays properties of both phases. This anisotropic
liquid is known as a liquid crystalline or mesomorphous
state. Using DSC, it is possible to observe the small energy
changes that occur as matter transitions from a solid to a
liquid crystal and from a liquid crystal to an isotropic liquid.

50.  Advantages
• Smaller sample required.
• Good qualitative data on phase changes.
 Disadvantages
• Limited to small sample size
• Thermograms are often complex and thus
difficult to interpret fully

51. COMPARISON OF DTA AND DSC
Aspect DSC DTA
Size of sample 2 to 10mg 20 to 50 mg
Sensitivity of
measurement of
heat of transition
A few joules/mole 0.5 Kj/mole
Heating and cooling
cycle
Programmed
heating and cooling
possible
Generally
programmed
heating.
Second order phase
transition
It can be observed
with a sample size
of 200mg
Not observed.
Specific heat
measurement
Accurate Not accurate