DIFFERNTIAL SCANNING COLORIMETRY

1. THERMAL
METHOD OF ANALYSIS
MAYANK MEHENDIRATTA
M.PHARM-2ND SEM.

2. INTRODUCTION….
Thermal method of Analysis can be defined as those techniques
where properties of material are studied when they change with the
temperature.
When matter is heated it will undergoes 2 changes-
1. PHYSICAL CHANGES- Phase changes such as melting, vapourization,
crystallization, trasition between crystal changes etc.
2. CHEMICAL CHANGES- Include reaction to form new products,
oxidation, decomposition, corrosion etc.

3. NOTE- THERMAL METHOD OF ANALYSIS can be used for qualitative and
quantitative analysis.
Information regarding detail structure and composition of different
phases of given sample
Temperature of phase changes, reaction, heat of the reaction are used
to determine the purity of material.

4. COMPARISON B/W DIFFERENT METHODS.

5. 1. THERMOGRAVIMETRY(T.G.A.) – A technique in which change in weight of
substance is recorded as a function of temperature.
2. DIFFERENTIAL THERMAL ANALYSIS(D.T.A.) – A technique in which temperature
difference between a substance and reference is measured as a function of
temperature.
3. DIFFERENTIAL SCANNING CALORIMETRY (D.S.C.) – A technique in which
difference in the energy inputs into substance and reference is measured as a
function of temperature.

6. DIFFERENTIAL SCANNING COLORIMETRY
 It is a thermal analysis technique in which difference in heat between the
specimen reference are measured against temperature/time while the
specimen is continuously heated under controlled conditions.
 This technique was developed by E.S. Watson and M.J.O. Neil in 1962.
 Function of calorimetry is to measure the heat content which comes in and out
of the sample.

7. INSTRUMENTATION
1. Sample Container: Sample container is designed in such a
a way that it can be used under high pressure and thermal
environment. For high temperature case platinum or
ceramic is used for sample holder and for low temperature
case aluminium is used.
2. Reference material: Generally reference material is made
up of calcined alumina Al2O3 or carborundum, silicon
carbide.
3. Temperature controller: Temperature controller is used to
maintain the temperature of the reference and sample at
the desired value. It is connected to computer centre.
4. Detector: In case of detector thermocouple is used to
measure the temperature change while the sample heated
under controlled environment .

8. PRINCIPLE
 Measuring principle is to compare the rate of heat flow to the sample and to the reference which are
heated at the same rate.
 To maintain the sample and reference at equal temperature during the physical transformations of the
sample (like phase transitions), either more or lesser amount of heat is required to be applied on it then
that required for the reference sample or an empty sample pan. This heat required depends on the nature
of the transformation process, that is, whether it is exothermic or endothermic.
 For instance, at a constant heating rate, when a solid sample changes to liquid, more heat is required to
be applied to the sample for increasing its temperature. This happens because heat is absorbed by the
sample while it changes state from solid to liquid. However, if there is exothermic process in the sample
(for instance, crystallization), less amount of heat is needed to increase the temperature of the sample.
 Thus, by calculating the heat flow differences between the reference and sample, DSC technique can
determine the amount of heat released or absorbed during a transition process.

9. TYPES OF D.S.C.
 Power Compensated DSC: In case of power compensated DSC, both reference and
sample are heated separately under different furnace.
 To rapidly heat, cool or maintaining equilibrium, small heating unit is required. The heating
unit needs to be integrated with a relatively larger temperature controlled heat sink. For
continuously monitoring the temperature of the material in reference and sample
holders,platinum resistance thermometeris used.
 The increasing the temperature, suitable power is applied to the reference and sample
heaters. This power required to maintain equal temperature of reference and sample is
recorded by the power compensated DSC as a function of temperature.
 Power compensated DSC has lower sensitivities than the heat flux DSC, however power
compensated DSC are faster than their heat flux counterparts.These instruments also have
higher resolution than the heat flux DSC.

11. HEAT COMPENSATED D.S.C.
 Here, both the reference and sample are heated under the same furnace.
 The difference between the temperatures of the reference and sample is recorded and converted
into a power difference and plotted against time or temperature.
 The main cell assembly of DSC is enclosed within a heated silver block cylinder, from which heat
is transmitted onto the specimen by a constantan disc connected to the cylinder. The reference
and sample pan are kept on two raised platforms in the system.
 The underside of both the platforms is connected to the constantan disc via connecting wires
and chromel (alloy of nickel and chromium) disks, thereby forming a thermocouple which is used
to measure the temperature difference between the two platforms. In addition to this, the
individual temperatures of the two platforms
 A set of mathematical equation converts signal into heat flow information.

13. GRAPH IN D.S.C .

14. FACTORS AFFECTING D.S.C. CURVE
 Instrumental factors: These include parameters such as – Furnace heating rate, furnace atmosphere,
recording speed, geometry of sample holders, location of sensors, sensitivity of the recording
system and material of the sample container.
 SAMPLE CHARACTERISTICS-
1. AMOUNT OF SAMPLE- About 0.5-10mg is usually sufficient. Small sample enable faster scanning
and it gives better peaks with good resolution and provide better contact with the environment.
2. SHAPE OF SAMPLE- Shape of sample has little effect on quantitative aspect . Samples in the form
of disc film/powder are preferred.