Material Research. ⢠The almost universal applicability of thermal analysis technique has led to their use in nearly every field of science, with a strong emphasis ...
Introduction to TG/DTA/DSC
Thermal Processing Technology Center Illinois Institute of Technology
Outline • • • • •
Introduction Theory of TG/DTA/DSC Application of TG/DTA/DSC TG/DTA/DSC in Metallurgy application Experiment difficulty
Application of Thermal Analysis in Material Research
• The almost universal applicability of thermal analysis technique has led to their use in nearly every field of science, with a strong emphasis on solving problems in materials technology and engineering, as well as "pure" scientific investigations. • The change in physical properties of a substance subjected to a controlled temperature program as a function of temperature is measured. • Techniques Include TG, DTA, DSC, DMA, TMA
Introduction to TG • Thermogravimetry is a technique measuring the variation in mass of a sample when it undergoes temperature scanning in a controlled atmosphere. This variation in mass can be either a loss of mass (vapour emission) or a gain of mass (gas fixation).
Introduction to DTA • Differential thermal analysis is a technique measuring the difference in temperature between a sample and a reference (a thermally inert material) as a function of the time or the temperature, when they undergo temperature scanning in a controlled atmosphere. The DTA method enables any transformation to be detected for all the categories of materials.
Introduction to DSC • Differential scanning calorimetry is a technique determining the variation in the heat flow given out or taken in by a sample when it undergoes temperature scanning in a controlled atmosphere. With heating or cooling any transformation taking place in a material is accompanied by a exchange of heat ; DSC enables the temperature of this transformation to be determined and the heat from it to be quantified.
Theory of TG (Thermogravimetry) • Measure the mass of sample as a function of temperature • Determine sample purity, decomposition behavior, chemical kinetics
Theory of DTA (Differential Thermal Analysis) • The temperature difference between reference and sample is monitored as a function of temperature
Theory of DSC (Differential Scanning Calorimetry) • The difference in heat flow to or from a sample and to or from a reference is monitored as a function of temperature or time, while the sample is subjected to a controlled temperature program Power compensated DSC
Theory of DSC (Differential Scanning Calorimetry) Temperatures are measured in thin plates in contact with those, thereby measuring the difference in heat flow from crucible. This gives a signal proportional to the difference in heat capacities between the sample and reference and thus the instrument will work as DSC. Heat flux DSC
Different principles of DSC signal detection
Different principles of DSC signal detection
The difference between DTA and DSC DTA Temperature difference is measured, amplified and recorded. The peak area can be converted to heat only if a suitable reference is used DSC The temperature difference is controlling the electrical power to the sample and reference in order to keep them at the same temperature. The peak area directly corresponds to the heat consumed or produced by the sample Modern DTA (also called heat flow DSC) Temperatures are measured in thin plates in contact with those, thereby measuring the difference in heat flow from crucible. This gives a signal proportional to the difference in heat capacities between the sample and reference and thus the instrument will work as DSC.
Application of TG • Study thermal degradation • Chemical reaction resulting in changes of mass such as absorption, adsorption, desorption • Sample purity
Application of DTA • Primarily used for detection of transition temperature • Sample purity
Application of DSC • Determination important transition temperatures • Determine heat of fusion of a crystal phase and the degree of crystallization • Study crystal kinetic • Determine heat capacity • Determine heat of formation • Sample purity
Summary TG Theory
Application
Measure the mass of sample
DTA Measure temperature difference between reference and sample
DSC Measure heat flow difference between reference and sample
TG
DTA
DSC
Mass change
Yes
No
No
Qualitative analysis of Heat change
No
Yes
Yes
Quantitative analysis of heat change
No
No
Yes
Program experiment temperature
DSC curve
TG-DTA curve of CuSO4-5H2O
Cp determination • Instruments calibrated by a standard Heat flow ( µ V)
Ab Ac
As
mc × (As − Ab) Cp = Cpc × ms × (Ac − Ab)
T time
Metallurgy Application Phase transformation and melting of Iron Heat Flow/ 1400.6 C
918.6 C
Exo
1533.7 C
-10 769 C -20 1404 C
1
2 Results • Different events may be observed during the heating : • at 769°C : curie point • at 924°C : α → γ transition • at 1400.6°C γ → δ transition • at 1533.7°C : melting of iron
Metallurgy application Oxydation of a steel in the scanning mode DTG/ %/min
TG./ %
0.08
0.06
0.5
0.04
0.0
0.02
TG
DTG 0.00
200
400
600
800
1000
Temperature/ 1200
Results Above 700C a mass gain is observed : the DTG shows two steps in the oxidation. Below 700C a mass loss is observed.
Metallurgy application Reduction of a steel at 1200C Temperature/
TG/ %
0.1
1300
Results T -0.0
1200
-0.1
1100
TG
-0.2
2.0
2.5
3.0
3.5
4.0
1000
Time/ h
At 1000C a small mass gain is observed due to traces of O2 and H2O. But when the temperature of 1200C is reached a strong mass decrease corresponding to the steel reduction is observed.
Metallurgy application Isothermal transformation of a high speed steel Temperature/
Heat Flow/ mW Exo 9
600
Results
Temperature 8
7
500
First heating
6
Second heating
400
5
300 4
3
200
2 100 1
0.5
1.0
1.5
2.0
2.5
3.0
Time/ h
When the temperature is stable at 560C a low exotherm can be observed, the DSC curve decreases slowly. After the isotherm of 3 hours the same sample is cooled then heated a second time in the same conditions. The difference between the two successive traces correspond to the sample transformation at 560C.
Metallurgy application Melting of a Cu-Ti intermetallic compound Heat Flow (µV) Exo 50
Results A double peak of melting is monitored.
0 1 -50
2
The onset peak of the first fraction is 925C.
932.9°C
The top of the second fraction is 978C.
-100 Onset point 1 : 925,2 °C Onset point 2 : 968.3 °C Enthalpy / J/g : 183.6 (Endothermic effect)
The total heat of melting is 183.6 J.g-1.
(34.0 + 149.6)
-150
-200
978.1°C
-250
500
600
700
800
900
1000
Temperature (°C)
Metallurgy aplication Melting of Pb-Sn alloy
H E AT F L OW /m W E xo 0
Results -5
1
2
-10
-15
Ent h
:
- 53.
T . On s e t
:
183.
Ent h1
:
- 20.
Ent h2
:
- 33.
Top
of
peak1
:
186.
Top
of
peak2
:
213.
-20 Sn/ Pb
:
The melting curve presents two peaks. In fact only pure substances melt presenting a 891 J/ g unique peak : generally alloys 5 C present a more complex 2 1 2 J / gmelting curve. In this case Pb 6 7 9 J / gan Sn present an eutectic at 9 C 183.5C. The end of melting corresponds to the liquids 2 C curve. M 119 presents the phase diagram of Pb-Sn system.
86/ 14
- - - - - - - - - - - - -25
T E MP E R ATU RE /°C -30
175
200
225
250
275
300
325
Metallurgy application Phase diagram of Pb-Sn system T E M P E R A T U R E /°C
Results 325
300
275
250
225
200
175
0 Pb
20
38
40
60
65
80
86
100 Sn
The onset temperature of the melting curve generally corresponds to the eutectic temperature of the system. The temperature of liquids is given by the top of the peak of melting.
Experiment difficulty Explanation of experiment result • Some curves might not be smooth and sharp System error • The error of commercialized instrument is about 5% • The measured thermodynamic property can be applied to modeling only if the error is less than 1% Crucible selection • Crucible should not • react with sample
Crucible material
Condition
Pt
Nonmetallic sample
Al2O3
Metallic sample
W
Reacting gas
BN Temperature setting • The higher temperature, the more problems - high sample vapor pressure - high sample diffusivity - short life time
Metallic sample
Setaram calorimeter Setsys1750: TG TG/DTA TG/DSC
Thermal analytical techniques, abbreviation and properties investigated Technique
