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Differential Scanning Calorimetry DSC

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Title: Differential Scanning Calorimetry DSC


1
Differential Scanning Calorimetry (DSC)
  • Bioanalytical Chemistry
  • Spring 2004

2
Thermal Analysis
  • Differential Scanning Calorimetry (DSC)
  • Measure heat absorbed or liberated during heating
    or cooling
  • Thermal Gravimetric Analysis (TGA)
  • Measure change in weight during heating or
    cooling
  • Thermomechanical Analysis (TMA)
  • Measure change in dimensions during heating or
    cooling

3
What Can You Measure with DSC?
  • Qualitative analysis
  • Fingerprinting of minerals, clays, polymers
  • Sample purity
  • Melting points
  • Heat capacity, cp
  • Glass transition temperature, Tg
  • Crystallization temperature, Tc
  • Phase diagrams

4
Where Used?
  • Pharmaceutical industry
  • Purity
  • Food industry
  • Characterization of fats and oils
  • Polymer industry
  • Synthetic blends

5
Schematic of DSC Instrument
Reference
Sample
T1
T2
Pt thermopile
Pt thermopile
Low mass 1 gram
heater
heater
N2 flow
DW
6
Variants of DSC
  • Heat flux
  • 1955 Boersma
  • 1 large (30 100 g) furnace
  • Power compensated
  • Separate small (1 g) microheaters for sample and
    reference
  • Hyper DSC
  • Very fast scan rates 500C/min
  • Mimic processing conditions
  • StepScan DSC
  • Short dynamic and isothermal scan steps
  • Separate reversible and irreversible effects

7
Output of DSC
Thermogram
exo
Glass transition
dH/dt, mJ/s
melting
crystallization
endo
Temperature, K
8
Heat Capacity
  • dqp/dt heat flow
  • dT/dt heating rate
  • (dqp/dt) / (dT/dt) dqp/dT cp

9
Temperature Program
  • T(t) T0 a twhere T is temperature, a is a
    constant and t is time
  • A t - Dynamic segment
  • dT/dt
  • T0 - Isothermal segment
  • Constant temperature

10
Glass Transition
Thermogram
  • Step in thermogram
  • Transition from disordered solid to liquid
  • Observed in glassy solids, e.g., polymers
  • Tg, glass transition temperature

Glass transition
dH/dt, mJ/s
Tg
Temperature, K
11
Crystallization
Thermogram
  • Sharp positive peak
  • Disordered to ordered transition
  • Material can crystallize!
  • Observed in glassy solids, e.g., polymers
  • Tc, crystallization temperature

Crystallization
dH/dt, mJ/s
Tc
Temperature, K
12
Melting
Thermogram
  • Negative peak on thermogram
  • Ordered to disordered transition
  • Tm, melting temperature
  • NB melting happens to crystalline polymers
    glassing happens to amorphous polymers

Melting
dH/dt, mJ/s
Tm
Temperature, K
13
Analysis
Crystallization
  • Sharp positive peak
  • Disordered to ordered transition
  • Observed in glassy solids, e.g., polymers
  • Tc, crystallization temperature

dH/dt, mJ/s
Tc
Temperature, K
14
Instrumental Performance
  • Blank test
  • No sample, no reference
  • Baseline provides info on
  • Sample contamination
  • Pt thermopile
  • 4,4-azoxyanisole standard
  • Netherlands Society for Thermal Analysis (TAWN)
  • 2 endothermic transitions
  • 117C
  • 134C
  • Resolution
  • Return to baseline
  • R 100 (1 ((dq/dt)min / (dq/dt)134C))
  • Sensitivity

15
Resolution
Thermogram
exo
dH/dt, mJ/s
endo
Temperature, K
16
Instrumental Specifications
  • Temperature range -170 to 730C
  • Accuracy/precision ?0.1C/?0.01C
  • Scan rates 0.01 to 500C/min
  • 1 g indium (10C/min, N2 purge)
  • Peak height 7.44 mW ? 0.15 mW
  • FWHM 0.42 ? 0.10C
  • H/W ratio 17.6 mW/C ? 1 mW/C
  • Isothermal drift (10 min)
  • -150C lt 15 µW
  • 100C lt10 µW

17
Sampling
  • Pan
  • Al
  • Au
  • Glass capillary tubes
  • Maximize contact between sample and pan
  • Thin films
  • Fine granules of uniform size
  • Grind!

18
Calibration
  • Calibrants
  • High purity
  • Metals
  • In 156.4C
  • Sn 231.9C
  • Pb 327.4C
  • Zn 419.5C
  • Al 660.4C
  • Inorganics
  • KNO3 128.7C
  • KClO4 299.4C
  • Organics
  • Triphenylmethane
  • Polystyrene 105C
  • Higher thermal conductivity than metals
  • Accurately known enthalpies
  • EX indium (5 10 mg)
  • ?H(fusion) 6.80 cal/g, mp 156.4C
  • K (Area/mass) ?H(fusion) 6.80 cal/g
  • Not hygroscopic
  • Not light sensitive
  • High thermal stability
  • Relatively unreactive
  • Pan
  • Atmosphere

19
Calibration
  • 1 point
  • 2 point
  • Is wide temperature range being used?

20
References
  • Mendham, J. Denney, R.C. Barnes, J.D. Thomas,
    M.J.K. Vogels Textbook of Quantitative Chemical
    Analysis 6th edition Prentice Hall Edinburgh,
    2000.
  • McNaughton, J.L. Mortimer, C.T. In IRS
    Physical Chemistry Series 2, 1975, 10, 1-44.
    Differential Scanning Calorimetry.
  • Differential Scanning Calorimetry. Avail. At
    URLwww.psrc.usm.edu/macrog/dsc.htm
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