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.
2. Types of thermal analysis
TG (Thermo Gravimetric) analysis: weight
DTA (Differential Thermal Analysis): temperature
DSC (Differential Scanning Calorimetry): energy
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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.
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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)
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5. Chemical:
• Oxidation (exothermic)
• Reduction (endothermic)
• Break down reactions
(endo – or exothermic)
• Chemisorption (exothermic)
• Solid state reactions
(endo – or exothermic)
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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).
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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
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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
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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
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33. Low thermal conductivity material Endothermic
High thermal conductivity material Exothermic
Ceramic holders & Metal holders
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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
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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
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41. DTA curve of silver nitrate
(a) Original sample
(b) The slightly ground sample
(c) The finely ground sample
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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
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45. • Peak area provide quantitative information regarding
the mass of the sample
∆𝐻𝑚 = 𝐾𝐴
• Calibration
𝐾 =
∆𝐻𝑚𝐶
𝐴∆𝑇𝑠
Heat of transition
Chart speed
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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
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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.
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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.
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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
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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
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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
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56. Disadvantages:
Relative low accuracy and precision (5-10 %)
Not be used for overlapping reactions
Need calibration over the entire temperature for DTA
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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.
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