2. 2
1. General Intr
oduction
2. Principle: W
h
a
t is D
S
C
?
3. V
arious techniques of D
S
C
4. Instrumentation a
n
d W
o
r
k
i
n
g of H
e
a
t Flux D
S
C
5. Factors Affecting to D
S
C Curve
6. Applications
3. 1. General Introduction
It is fundamental tool in Thermal Analysis
It is widely used in many industries from-
Food, Pharmaceticals, Polymers, Agriculture, nanomaterials,
etc. 2. What is DSC?
3
It is thermal technique in which,
The heat or energy necessary to establish a zero temperature
difference between sample and reference is measured as
a
function of temperature or time, when both are heated or
cooled
at predetermined rate.
4. Various Techniques of DSC
4
A) Heat Flux DSC
Single heater is used to heat Sample and reference
Allow tempt. Between Sample and Reference
to
vary.
This diff. in tempt is used to get required
heat flow.
Less sensitive
Slower heating and cooling rates
Less accurately measures heat capacity
and enthalpy.
5. B) Power Compensated DSC
Two identical and separate heaters are used
Tempt. Diff. during phase transition or reaction
in the sample are compensated by varying
electrical
current supplied to heaters.
The supplied electrical current is
directly proportional to heat absorbed during
process.
Gives Better resolution
Rapid cooling and heating
5
7. HEAT FLUX DSC
Sample holder: platinum,
aluminum and stainless
Steel.
Sensors: Temperature
sensors.
Usually thermocouples
which are same for both
sample and reference.
Furnace: one block for both
reference and sample cell.
POWER COMPENSATION DSC
Sample holder : platinum,
aluminum and stainless
steel pans.
Sensors: platinum
resistance thermocouple.
Separate sensors and
heaters for both reference
and sample.
Furnace: separate block for
both reference and sample
cell
8. 4. Instrumentation & Working of Heat Flux DSc
• Consist of Cylindrical Silver heating block
• This block gives heat to the specimen via constantan thermoelectric disc
• The disc has two raised platfoms on which ‘S’ & ‘R’ placed
• Underside of each platform chromel disc is attached
• Chromel-constantan thermocouple used to measure differential tempt
• Alumel- Chromel thermocouple determines individual tempt of S & R
• Thermocouple embedded in Silver block, acts as tempt controller for programmed heating cycle.
• Inert gas passed at const. flow 40 ml per min.
10. Working of DSC
10
S & R sealed in Al or Cu pan
Placed adjacent to each other
Common heating applied to both
Heater heats S & R at const rate and sensor senses
tempt
Now sample tends to absorb or release heat due to
transitions & tempt varies
Tomaintain constanttempt more or less heat
supplied to sample
The amt of heat transferred to sample is monitored by
PC and output received in the form of thermogram.
11. Accurately-weigh (2-30mg)
• Small sample pans (0.1 mL) of inert or treated metals (Al, 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
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
Keiselguhr is another reference material normally used when sample has a
fibrous nature
Reference material
Sample
13. 5. Factors affecting to DSC Curve
13
A) Instrumental Factors
• Heating rate
• Geometry of Sample & Location of
sensor
• Recorder or chart speed
• Sensitivity of recorder
• Furnace atmosphere
• Material of sample holder
A) Sample Characteristics
• Amount
• Size of Particle
• Nature
• Compactness
• Heat of reaction
• Thermal conductivity
•Solubility of evolved gases in
14. Rapidity of the determination
Small sample masses
Versatility
Simplicity
Applicability
Study many types of chemical reactions
No of Need calibration over the entire temperature for DSC
Relative low accuracy
Not be used for overlapping reactions.
Difficulties in test cell preparation in avoiding evaporation of
volatile Solvents
Does not detect gas generation
Disadvantages
Advantages
15. 6. Applications
15
Sr.
No
Industry Transition
s
Purpose
1. Pharmac
eticals
Tg Storage tempt, amorphous
content
Cp Processing conditions
Tm Polymorphs, purity , QC
2. Polymers Tg Processing, Material
Property, effect of additives
Tm Polymer processing, heat
history
Exotherm Reaction rate, curing of
materials, etc.
Cp Energy needed to process
Tc Recrystallization time, kinetics
3. Food Tg Storage tempt, other
properties
Tm Processing tempt.
16. 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
• Choosing better solvent
• Liquid crystals
• Oxidative stability
• Safety screening
• Drug Analysis
• General chemical
analysis
• Food science
• Polymers
• Metals
• Protein analysis
APPLICATIONS
