Thermal Processing Technology CenterIllinois Institute of Technology

Introduction to TG/DTA/DSC

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 analysistechnique 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 afunction 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 undergoestemperature 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 placein 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 sampleis 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 areference is monitored as a function of temperature or time, while thesample 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. Thisgives a signal proportional to the difference in heat capacitiesbetween 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 DSCDTA

Temperature difference is measured, amplified and recorded. The peak area can be converted to heat only if a suitable reference is used

DSCThe 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 bythe sample

Modern DTA (also called heat flow DSC)Temperatures are measured in thin plates in contact with those, therebymeasuring 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

Measure heat flowdifference betweenreference and sample

Measure temperaturedifference betweenreference and sample

Measure the mass of sample

Theory

DSCDTATG

YesNoNoQuantitative analysis ofheat change

YesYesNoQualitative analysis ofHeat change

NoNoYesMass change

DSCDTATGApplication

Program experiment temperature

DSC curve

TG-DTA curve of CuSO4-5H2O

Cp determination• Instruments calibrated by a standard

C Cp p= × × −× −

c

m (A A )m (A A )

c s b

s c b

time

Heat flow ( V)

Ab

As

T

Ac

µ

Metallurgy ApplicationPhase transformation and melting of Iron

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

Temperature/200 400 600 800 1000 1200

Heat Flow/

-80

-70

-60

-50

-40

-30

-20

-10

Exo

769 C

924 C

1404 C

1551 C

918.6 C 1400.6 C 1533.7 C

1 : Point de curie

2 : Transition alpha --> Gamma

3 : Transition Gamma --> Delta

4 : Fusion

1

2

3

4

Metallurgy applicationOxydation of a steel in the scanning mode

Temperature/200 400 600 800 1000 1200

TG./ %

0.0

0.5

DTG/ %/min

0.00

0.02

0.04

0.06

0.08

TG

DTG

ResultsAbove 700 C a mass gain is observed : the DTG shows two steps in the oxidation.Below 700 C a mass loss isobserved.

Metallurgy applicationReduction of a steel at 1200 C

Time/ h2.0 2.5 3.0 3.5 4.0

TG/ %

-0.2

-0.1

-0.0

0.1

Temperature/

1000

1100

1200

1300

T

TG

Results

At 1000 C a small mass gainis observed due to traces ofO2 and H2O. But when thetemperature of 1200 C isreached a strong massdecrease corresponding to thesteel reduction is observed.

Metallurgy applicationIsothermal transformation of a high speed steel

First heating

Time/ h0.5 1.0 1.5 2.0 2.5 3.0

Heat Flow/ mW

1

2

3

4

5

6

7

8

9

Temperature/

100

200

300

400

500

600

Exo

Second heating

Temperature Results

When the temperature isstable at 560 C a lowexotherm can be observed,the DSC curve decreasesslowly.

After the isotherm of 3 hoursthe same sample is cooledthen heated a second time inthe same conditions.

The difference between thetwo successive tracescorrespond to the sampletransformation at 560 C.

Metallurgy applicationMelting of a Cu-Ti intermetallic compound

500 600 700 800 900 1000

-250

-200

-150

-100

-50

0

50

Exo

Onset point 1 : 925,2 °COnset point 2 : 968.3 °C

Enthalpy / J/g : 183.6 (Endothermic effect) (34.0 + 149.6)

932.9°C

978.1°C

1 2

Heat Flow (µV)

Temperature (°C)

Results

A double peak of melting ismonitored.

The onset peak of the firstfraction is 925 C.

The top of the second fractionis 978 C.

The total heat of melting is183.6 J.g-1.

Metallurgy aplicationMelting of Pb-Sn alloy

175 200 225 250 275 300 325-30

-25

-20

-15

-10

-5

0

Exo

- - - - - - - - - - - - -

S n / P b : 8 6 / 1 4

T o p o f p e a k 2 : 2 1 3 . 2 C

T o p o f p e a k 1 : 1 8 6 . 9 C

E n t h 2 : - 3 3 . 6 7 9 J / g

E n t h 1 : - 2 0 . 2 1 2 J / g

T . O n s e t : 1 8 3 . 5 C

E n t h : - 5 3 . 8 9 1 J / g

1 2

H EAT FLOW/mW

TEMPER ATU RE/°C

Results

The melting curve presentstwo peaks. In fact only puresubstances melt presenting aunique peak : generally alloyspresent a more complexmelting curve. In this case Pban Sn present an eutectic at183.5 C. The end of meltingcorresponds to the liquidscurve. M 119 presents thephase diagram of Pb-Snsystem.

Metallurgy applicationPhase diagram of Pb-Sn system

2 0 4 0 6 0 8 0 1 0 0

1 7 5

2 0 0

2 2 5

2 5 0

2 7 5

3 0 0

3 2 5

T E M P E R A T U R E / ° C

S n0

P b 3 8 6 5 8 6

Results

The onset temperatureof the melting curvegenerallycorrespondsto the eutectictemperatureof the system. Thetemperatureof liquids is given by the top of the peak of melting.

Experiment difficultyExplanation 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

Temperature setting• The higher temperature, the more problems

- high sample vapor pressure- high sample diffusivity- short life time

Metallic sampleBN

Reacting gasW

Metallic sampleAl2O3

Nonmetallic samplePt

ConditionCrucible material

Setaram calorimeter

Setsys1750:

TG

TG/DTA

TG/DSC

Thermal analytical techniques, abbreviation andproperties investigated

Technique Abbreviation Physical Properties• thermodilatometry - length• Thermogravimetry TG(TGA) mass• Derivative thermogravimetry DTG mass• Differential Thermal Analysis DTA temperature• Differential Scanning Calorimetry DSC enthalpy• Thermomechanical Analysis TMA dimension• Dynamic Mechanical Analysis DMA stiffness & damping• Thermally Stimulated Current TSC dipole alignment/relaxation• Dielectric Analysis DEA dielectric permittivity/loss factor• Evolved Gas Analysis EGA gaseous decomposition products

• Thermo-optical Analysis TOA optical properties