This document discusses several thermal analysis techniques including differential thermal analysis (DTA). It explains that DTA involves heating a sample and inert reference material simultaneously and measuring any temperature difference, which can indicate physical or chemical changes in the sample. The document provides details on DTA instrumentation, the factors that can affect DTA results, and applications such as material identification and purity assessment by comparing DTA curves.

1. 1
BY
Dr. Suman Pattanayak
Associate Professor
Department of Pharma Analysis & QA.
Vijaya Institute of Pharmaceutical Sciences for Women
M. Pharm/ I Sem
Advance Pharmaceutical Analysis

2. Different Techniques
• Thermometric Titration (TT)
– Heat of mixing
• Thermal Mechanical Analysis (TMA)
– Thermal Expansion Coefficient
• Dynamic Mechanical Analysis (DMA)
– Viscoelastic Properties
• Differential Scanning Calorimetric (DSC)
– Heat flow during Transitions
• Thermal Gravimetric Analysis (TGA)
– Weight Loss due to decomposition
– Derivative Thermogravimetric Analysis (DTG)
• Differential Thermal Analysis (DTA)
– Heat of Transitions
• Temperature Programmed Desorption (TPD)
– Temperature at which gas is desorbed from (catalyst) surface
– Emission gas Thermoanalysis (EGT)

3. Basic Principle
• Sample is heated at a constant heating
rate
• Sample’s Property Measured
– Wt TGA
– Size TMA
– Heat Flow DSC
– Temp DTA
– Gas evolved TPD

4. TGA
• Constant Heating
Rate
– Initial Temp
– Final Temp
– Heating Rate (°C/min)
• Data
– Weight vs Time
– Weight vs Temp.
• Differential This Data
(DTG)

5. DSC

6. DSC
• Constant Heating Rate
– Initial Temp
– Final Temp
– Heating Rate (°C/min)
• Data
– Heat flow to sample minus
Heat flow to reference vs
Time (Temp.)
• Measures heat of
crystallization
Polymer without weight change in this temperature range

7. DTA
• Sample and Reference Placed in Heater
• Constant Heating Rate
– Initial Temp
– Final Temp
– Heating Rate (°C/min)
• Data
– Temp of Sample vs Time (or Temp)
– Temp of Reference vs Time (or Temp)
– Reference should be inert, e.g. nothing but latent heat
• Measures
– Heat of crystallization
– Glass Transition Temperature

8. DTA + DTG

9. TMA
• Constant Heating Rate
– Initial Temp
– Final Temp
– Heating Rate (°C/min)
• Data
– Size of Sample vs Time (or Temp.)
• Measures
– Thermal Expansion Coefficient
– Volume change on crystalization or crystal
transformations
– Sintering
– Glass Transitions in Polymers

10. TMA
Polymer with glass transition

11. DMA
• Constant Heating Rate
– Initial Temp
– Final Temp
– Heating Rate (°C/min)
• Data
– Force vs Time (or Temp.)
– Force delay vs Time (or
Temp.)
– Viscoelastic Properties
• Storage and Loss Modulus
• Measures
– Glass Transition
– Viscoelastic Properties Polymer with Glass Transition

12. We have TGA - only
• Heating a sample of Calcium oxalate
• Ca(C204)*xH2O  Ca(C204) *H2O + x-1 H2O
• Ca(C204)*H2O Ca(C204) + H2O
• Ca(C204)  CaCO3 + CO
• CaCO3  CaO + CO2

13. TGA
• Constant Heating
Rate
– Initial Temp
– Final Temp
– Heating Rate (°C/min)
• Data
– Weight vs Time
– Weight vs Temp.
• Differential This Data
(DTG)

14. TGA – Ca(C204)*xH2O

15. Different Heating Rates

16. Heating Rate
• Heating Too Fast
– Overlaps Transitions
• Interpretation Problems
• Kinetics of Decomposition
– Sample Size
– Mass Transfer
• Convective Mass Transfer
• Pore Diffusion
– Heat Transfer
• Convective Heat Transfer
• Thermal Conductivity
– Porous solid

17. Precipitated Zr5O8(SO4)2*15 H2O
This sample was dried fro 48 hrs at 110C before TGA analysis.
What is going on?

18. Analysis of Filtrate from
Precipitation
• Precipitation
• 5ZrOCl2 + 2H2SO4 + xH2O 
Zr5O8(SO4)2*15 H2O (s) + 10 HCl
• Decomposition
• Zr5O8(SO4)2*15 H2O (s) 
Zr5O8(SO4)2*14 H2O (s) + H2O (v)
• Zr5O8(SO4)2  5
ZrO2 (s) +2 SO2 (v)

19. INTRODUCTION
• This is a comparison method
• Analytical method for recording the
difference in temperature (∆T) b/w a
substance and an inert reference material as
a function of temperature or time
• Any transformation – change in specific heat
or an enthaply of transition can be detected
by DTA

20. • In DTA both test sample & an inert reference
material (alumina) – controlled heating or
cooling programming
• If zero temperature difference b/w sample &
reference material – sample does not
undergo any chemical or physical change.
• If any reaction takes place temperature
difference (∆T) will occur b/w sample &
reference material

21. • A DTA curve can be used as a finger print for
identification purposes, for example,
• in the study of clays where the structural
similarity of different forms renders diffraction
experiments difficult to interpret.

22. ∆T VS Temp.
Sharp Endothermic – changes in crystallanity or fusion
Broad endotherms - dehydration reaction
Physical changes usually result in endothermic curves
Chemical reactions are exothermic

23. Apparatus
• The key features of a differential thermal analysis
kit are as follows
1. Sample holder comprising thermocouples,
sample containers and a ceramic or metallic
block.
2. Furnace.
3. Temperature programmer.
4. Recording system.

27. • Heart of the analysis – heating block
• Identical pair of cavities for the sample, ref.
material
• Whole unit is set in an oven- control pressure
• Thermocouple is place directly in contact with
the sample and another in contact with the
reference
• Temp.of the block is raised, the temperature of
the sample & reference follow
• Zero temp. difference – no physical or chemical
change
• If any reaction – difference in ∆T

30. Differential Thermal Analysis
advantages:
• instruments can be used at very high
temperatures
• instruments are highly sensitive
• characteristic transition or reaction
temperatures can be accurately
determined
disadvantages:
• uncertainty of heats of fusion, transition,
or reaction estimations is 20-50%
DTA

31. Factors affect results in DTA
• Sample weight
• Particle size
• Heating rate
• Atmospheric conditions
• Conditions of sample packing into dishes

33. Applications
• Quantitative identification and purity
assessment of materials are accomplished by
comparing the DTA curve of sample to that of
a reference curve
• Impurities may be detected by depression of
the M.P