This document discusses differential thermal analysis (DTA), which measures the difference in temperature between a sample and a reference material as both are heated. It describes phenomena like physical changes (melting, vaporization) and chemical reactions that cause temperature changes detectable by DTA. Instrumentation for DTA is also outlined, including furnaces, temperature programmers, and amplifiers. Factors that can affect DTA curves like heating rate, atmosphere, sample mass, and particle size are examined. Differential scanning calorimetry (DSC) is also introduced as a related technique.

1. By: z. mohammadpour

2. Types of thermal analysis
TG (Thermo Gravimetric) analysis: weight
DTA (Differential Thermal Analysis): temperature
DSC (Differential Scanning Calorimetry): energy
2

3. Differential Thermal Analysis (DTA)
Introduction:
Differential thermal
analysis is a technique in
which the difference in
temperature between a
substance and reference
material is measured as a
function of temperature
while the sample and
reference are subjected to
controlled temperature
programme.
3

4. Phenomena causing changes in temperature
Physical:
• Adsorption (exothermic)
• Desorption (endothermic)
• A change in crystal structure
(endo – or exothermic)
• Crystallization (exothermic)
• Melting (endothermic)
• Vaporization (endothermic)
• Sublimation (endothermic)
4

5. Chemical:
• Oxidation (exothermic)
• Reduction (endothermic)
• Break down reactions
(endo – or exothermic)
• Chemisorption (exothermic)
• Solid state reactions
(endo – or exothermic)
5

6. 6

7. Comparison between TA & DTA
7

8. Historical aspects:
In 1899 Robert Austen improved
this technique by introducing two
thermocouples, one placed in
sample and other in the reference
block.
This technique was later on
modified by Burgess(1909),
Norton(1939), Grim(1951),
Kerr(1948), Kauffman(1950), Fold
Vari(1958).
8

9. DTA systems:
9

10. Instrumentation:
10

11. 11

12. 2. Furnace Assembly
12

13. 3. Temperature
programmer
4. Amplifier
and recorder
13

14. Theoretical Aspects
1. Speil theory
m(ΔH)/gk= 𝑡1
𝑡2
∆𝑇 𝑑𝑡
14

15. 2. Boersma equation
I. Cylinder geometry
𝑡1
𝑡2
∆𝑇 𝑑𝑡 =
𝑞𝑎2
4λ
II. Spherical geometry
𝑡1
𝑡2
∆𝑇 𝑑𝑡 =
𝑞𝑎2
6λ
15

16. III. Flat plate geometry
𝑡1
𝑡2
∆𝑇 𝑑𝑡 =
𝑞𝑎2
2λ
IV. Large ceramic block
𝑡1
𝑡2
∆𝑇 𝑑𝑡 =
𝑞𝑎2
6
2
λ 𝑐
+
1
λ 𝑠
16

17. V. Metal cups
𝑡1
𝑡2
∆𝑇 𝑑𝑡 =
𝑚𝑞
𝐺
17

18. 3. Pacor expression
1
𝑎 𝑟
𝜕𝑇𝑟
𝜕𝑡
= 𝛻2 𝑇𝑟
1
𝑎 𝑠
𝜕𝑇𝑠
𝜕𝑡
= 𝛻2
𝑇𝑠 +
1
λ
𝑄
𝛻2
𝑡1
𝑡2
∆𝑇 − ∆𝑇1
𝑑𝑡 =
𝑄
λ
= 𝛻2
𝑆
𝛼
18

19. 4. Gray general theory
𝑅
𝑑𝐻
𝑑𝑡
= 𝑇𝑠 − 𝑇𝑟 + R 𝐶𝑠 − 𝐶𝑟
𝑑𝑇𝑟
𝑑𝑡
+ 𝑅𝐶𝑠 𝑑
𝑇𝑠 − 𝑇𝑟
𝑑𝑡
I II III
19

20. 20

21. Factors affecting DTA curves:
DTA is a dynamic temperature technique.
Therefore, a large number of factors can
affect. These factors can be divided into the
two groups:
i) Instrumental factors
ii) Sample factors
21

22. Instrumental factors :
Furnace atmosphere
Furnace size and shape
Sample holder material
Sample holder geometry
Wire and bead size of thermocouple junction
Heating rate
Speed and response of recording instrument
Thermocouple location in sample
22

23. Sample characteristic :
Particle size
Thermal conductivity
Heat capacity
Packing density
Swelling or shrinkage of sample
Amount of sample
Effect of diluent
Degree of crystallinity
23

24. Heating rate
𝑑 𝑙𝑛 𝛽 ∆𝑇2
𝑚𝑖𝑛
𝑑 1 ∆𝑇 𝑚𝑖𝑛
= −
𝐸
𝑅
Heating rate
24

25. Heating rate
25

26. Effect of heating
rate on curve peak
resolution,
compound used
was cholesterol
propionate.
26

27. Effect of heating
rate on the peak
amplitude,
compound used
was cholesterol
propionate.
27

28. Furnace atmosphere
𝐴 𝑠𝑜𝑙𝑖𝑑 𝐵𝑠𝑜𝑙𝑖𝑑 + 𝐶𝑔𝑎𝑠
An approximation form of Van’t Hoff equation:
𝑙𝑛
𝐾 𝑝 2
𝐾 𝑝 1
= 𝑙𝑛
𝑃𝑐 2
𝑃𝑐 1
=
∆𝐻 𝑇2 − 𝑇1
𝑅 𝑇2 𝑇1
28

29. Generally two types of gaseous
atmosphere are employed:
a. A static gaseous atmosphere
b. A dynamic gaseous atmosphere
29

30. Effect of O2 and N2
atmosphere on the
DTA curve of a
mixture of 2.5%
lignite in Al2O3.
30

31. Effect of atmosphere on the thermal decomposition of
SrCO3.
𝑠𝑜𝑙𝑖𝑑1
𝑎𝑡 927℃
𝑠𝑜𝑙𝑖𝑑2
31

32. Sample holder
• Effect of sample holder
diffusivity on the shape
of the DTA peak.
32

33. Low thermal conductivity material Endothermic
High thermal conductivity material Exothermic
Ceramic holders & Metal holders
33

34. Comparison of block and isolated container
sample holders
advantages disadvantages
Block type
1. Good temperature uniformity
2. Good thermal equilibration
3. Good resolution
4. God for b.p. determinations
1. Poor exchange with atmosphere
2. Poor calorimetric precision
3. Difficult sample manipulation
4. Sensitive to sample density change
Isolated container type
1. Good exchange with atmosphere
2. Good calorimetric precision
3. Good for high temperature use
1. Poor resolution
34

35. Thermocouples
𝑄 =
𝑡1
𝑡2 𝐴λ 𝑝
𝑙
θ0dt
𝑡1
𝑡2
𝜃0 dt =
𝑞𝑎2
6λ
.
𝛼
1 + Λ λ
35
𝝀 𝒑 𝜶

36. Thermocouple location
36

37. Effect of having an asymmetric arrangement of sample
and reference thermocouples
(a) Thermocouple 0.06 cm from center of sample
(b) Thermocouple 0.3 cm from center of sample
37

38. System temperature versus ΔT for carborundum in
both cells
38

39. Sample mass
𝐴 ∝
𝜑𝑟2
∆𝐻𝑙
𝑘
𝐴 =
𝐺𝑚∆𝐻
𝑘
39
Sample mass

40. Sample particle size
40

41. DTA curve of silver nitrate
(a) Original sample
(b) The slightly ground sample
(c) The finely ground sample
41

42. Effect of diluent
• Masking effect of sample peaks caused by diluent
(a) 8-quinolonol diluted
to 6.9% with carborundum
(b) 8-quinolinol diluted
to 5.9% with alumina
42

43. Key operational parameters
43

44. Factors that influence DTA curve
44

45. • Peak area provide quantitative information regarding
the mass of the sample
∆𝐻𝑚 = 𝐾𝐴
• Calibration
𝐾 =
∆𝐻𝑚𝐶
𝐴∆𝑇𝑠
Heat of transition
Chart speed
45

46. Calibration standards
46

47. Differential Scanning Calorimetery (DSC)
• DSC measures differences in the amount of heat required to
increase the temperature of a sample and a reference as a function
of temperature 47

48. Control loupes in DSC
sample reference
Differential temperature control loop to
maintain temperature of the two pan
holders always identical
Average temperature control loop to give
predetermined rate of temperature increase
or decrease
48

49. Power compensated DSC: Temperature differences
between the sample and reference are ‘compensated’ for by
varying the heat required to keep both pans at the same
temperature. The energy difference is plotted as a function
of sample temperature.
49
Platinum sensors
Sample heater Reference heater

50. Heat flux DSC utilizes a single furnace. Heat flow into both
sample and reference material via an electrically heated
constantan thermoelectric disk and is proportional to the
difference in output of the two thermocouple junctions.
50

51. Differential Scanning Calorimetry
PET
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 50 100 150 200 250 300 350
Temperature (C)
HeatFlow(W/gm)
Melting
Glass Transition
Crystallization
ENDOTHERMIC
EXOTHERMIC
Sample: Polyethylene terephthalate (PET)
Temperature increase rate: 20°C/min
Temperature range: 30°C - 300°C 51

52. Quantitative DSC:
𝑎𝑟𝑒𝑎 = 𝐾∆𝐻𝑚
52
Independent of temperature

53. 6
Influence of Sample Mass
Temperature (°C)
150 152 154 156
0
-2
-4
-6
DSCHeatFlow(W/g)
10mg
4.0mg
15mg
1.7mg
1.0mg
0.6mg
Indium at
10°C/minute
Normalized Data
158 160 162 164 166
Onset not
influenced
by mass
53

54. 6
Effect of Heating Rate
on Indium Melting Temperature
154 156 158 160 162 164 166 168 170
-5
-4
-3
-2
-1
0
1
Temperature (°C)
HeatFlow(W/g)
heating rates = 2, 5, 10, 20°C/min
54

55. Advantages:
Rapidity of the determination
Small sample masses
Versatility
Simplicity
Applicable
Study many types of chemical reactions
No of Need calibration over the entire temperature for
DSC
55

56. Disadvantages:
Relative low accuracy and precision (5-10 %)
Not be used for overlapping reactions
Need calibration over the entire temperature for DTA
56

57. References:
P. J. Elving & I. M. Kolthoff, Chemical analysis, Vol. 19,
P134, 1964.
H. Faghihian, S. Shahrokhian, H. Kazemian, thermal
methods of analysis, P81, 2006.
G. klancnik, J.Medved, P. Mrvar., Materials and
Geoenvironment, Vol. 57, No. 1, pp. 127–142, 2010.
57

58. ?
58