DSC

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

1 : Point de curie -40

3

924 C

-30

2 : Transition alpha --> Gamma 3 : Transition Gamma --> Delta 4 : Fusion

-50

-60

-70

4 -80 1551 C 200

400

600

800

1000

1200

Temperature/


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

Metallurgy application Reduction of a steel at 1200
C 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 1000
C a small mass gain is observed due to traces of O2 and H2O. But when the temperature of 1200
C 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 560
C 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 560
C.

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 925
C.

932.9°C

The top of the second fraction is 978
C.

-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 183.5
C. 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

Abbreviation

• • • • • • • • • •

thermodilatometry Thermogravimetry Derivative thermogravimetry Differential Thermal Analysis Differential Scanning Calorimetry Thermomechanical Analysis Dynamic Mechanical Analysis Thermally Stimulated Current Dielectric Analysis Evolved Gas Analysis

TG(TGA) DTG DTA DSC TMA DMA TSC DEA EGA

•

Thermo-optical Analysis

TOA

Physical Properties length mass mass temperature enthalpy dimension stiffness & damping dipole alignment/relaxation dielectric permittivity/loss factor gaseous decomposition products optical properties