PM DR KHAIREL : THERMAL ANALYSIS : METALS

THERMAL ANALYSIS
: METALS

ASSOC. PROF. DR. KHAIREL RAFEZI AHMAD, AMP (Perlis)

B.Eng. (USM), MSc. (USM), PhD. (USM), Certified NLP (ANLP),

METAL

Thermal Properties

• The properties of a material
that determine how it reacts
when it is subjected to
excessive heat, or heat
fluctuations over time are
called thermal properties.

Thermal Properties

• We shall take a look at the
following thermal properties :
oHeat Capacity
oThermal Expansion
oThermal Conductivity
oThermal Stress

Thermal Properties 4

HEAT CAPACITY THERMAL EXPANSION

Heat capacity represents the When the temperature of a
amount of energy required to material increases, a change
produce a unit temperature (usually expansion) in its
rise. length or volume is observed,
this change is known as thermal
THERMAL CONDUCTIVITY expansion.

The property that characterizes THERMAL STRESS
the ability of a material to
transfer heat is called thermal The stress induced in a
conductivity. body as a result of changes
in temperature is called
thermal stress.

What is Thermal Analysis?

Thermal Analysis is the term applied to a
group of methods and techniques in which
chemical or physical properties of a
substance, a mixture of substances or a
reaction mixture are measured as function
of temperature or time, while the
substances are subjected to a controlled
temperature programme

Or

Techniques in which a thermal property of a
substance is measured as a function of
temperature or time while the substance is
subjected to a controlled temperature
variation.

Thermal Analysis instrument includes the
followings:

 Detection Unit: Furnace, sample and
reference holder, and sensor, heat and
cool the sample in the furnace, and
detects the sample temperature and
property.

 Temperature Control Unit: Controls the
furnace temperature.

 Data Recording Unit: Records the
signals of sensor and sample temperature,
and analyses them.

THERMAL ANALYSIS
 The atmosphere of furnace:

- Static air (inert condition) – nitrogen, argon, vacuum >
inhibit oxidation
- Static air (oxidizing condition) - oxygen
- Continuous flow of gas (purging) – i.e for reducing
condition, purging of hydrogen

Some of Thermal Analyses Method

• Differential Scanning • Isothermal Calorimetry (TAM)
Calorimetry (DSC) • Thermomechanical Analysis

• Thermogravimetric Analysis (TMA)
(TGA) • Flash Diffusivity
• Thermal Conductivity
• Vapor Sorption Analysis (SA) • Dilatometry (DIL)

• Dynamic Mechanical Analysis
(DMA)

• Rheometer

Common Thermal Analyses Method

Table shows the measurement techniques for each property. Each technique is called DTA, DSC, TG,
DIL and DMA.

Abbrev. TA Measurement Technique Property Unit

DTA Differential Thermal Analysis Difference temperature °C or µV*

DSC Differential Scanning Enthalpy W = J/sec
Calorimetry

TG Thermogravimerty Mass gram

DIL Dilatometry Analysis Deformation meter

DMA Dynamic Mechanical Elasticity Pa = N/m2
Analysis

Table shows which effects and properties found in various materials are measured in each

technique.

Phenomenon/Property DSC Technique DMA

TG DIL

Melting ⚪— Δ Δ

Glass transition ⚪ — ⚪ ⚪

Crystallization ⚪— Δ ⚪

Reaction (Curing / ⚪ Δ ⚪ ⚪
Polymerization)

Sublimation / Evaporation / Δ ⚪ — —
Dehydration

Thermal decomposition Δ ⚪ — —

Thermal expansion / — — ⚪ —
Thermal shrinkage

Thermal history ⚪ — ⚪ ⚪

Specific heat capacity ⚪ — — —

⚪: Measurement Object Δ: Some compatible —: Not measured

THERMAL ANALYSIS 11

4 MAIN THERMAL METHODS

Thermogravimetry Analysis (TGA)

- mass

Differential Scanning Calorimetry (DSC)

- enthalpy

Dynamic Mechanical Analysis (DMA)

- viscoelastic properties

Dilatometry Analysis (DIL)

- Deformation

v

12

TMERMAL ANALYSIS

Thermogravimetry
Analysis (TGA)

• TGA measures amount and rate of
weight change vs. temperature or
time in a controlled atmosphere.

• Characterizes materials that exhibit

weight loss or gain due to

decomposition, oxidation, or

dehydration.

What is Thermogravimetric Analysis (TGA)?

• Thermogravimetric Analysis (TGA) measures weight/mass
change (loss or gain) and the rate of weight change as a function
of temperature, time and atmosphere.

• Measurements are used primarily to determine the composition of
materials and to predict their thermal stability. The technique
can characterize materials that exhibit weight loss or gain due to
sorption/desorption of volatiles, decomposition, oxidation and
reduction.

What TGA Can Tell You?

• Thermal Stability of Materials • Decomposition Kinetics of
Materials
• Oxidative Stability of Materials
• The Effect of Reactive or
• Composition of Multi-component Corrosive Atmospheres on
Systems Materials

• Estimated Lifetime of a Product • Moisture and Volatiles Content
of Materials

General considerations

Suitable samples for TG are solids that undergo one of
the two general types of reaction:

Reactant(s)  Product(s) + Gas (a mass loss)
Gas + Reactant(s)  Product(s) (a mass gain)

Processes occurring without change in mass (e.g., the
melting of a sample) obviously cannot be studied by
TG.

Mechanisms of Weight Change in TGA

• Weight Loss:

• Decomposition: The breaking apart of chemical bonds.
• Evaporation: The loss of volatiles with elevated temperature.
• Reduction: Interaction of sample to a reducing atmosphere

(hydrogen, ammonia, etc).
• Desorption: a substance is released from a surface.

• Weight Gain:

• Oxidation: Interaction of the sample with an oxidizing
atmosphere.

• Absorption: absorbing something or of being absorbed.

All of these are kinetic processes (i.e. there is a rate at which they

occur).

Types of Thermogravimetry analysis (TGA)

 There are different types ofTGA available:
1. Isothermal or Static TGA: In this case, sample is

maintained at a constant temperature for a period
of time during which change in weight is recorded.
2. Quasi-static TGA: In this technique, the sample is heated
to a constant weight at each of a series of increasing
temperature.
3. Dynamic TGA: In this type of analysis, the sample is
subjected to condition of a continuous increase in
temperature at a constant heating rate, i.e., usually
linear with time.

Instrumentation

Figure 1: Block Diagram of a Thermobalance.

 The instrument used forTGA analysis is a programmed precision
balance for a rise in temperature (called as Thermobalance)

 Thermobalance consists of an electronic microbalance
(important component), a furnace, a temperature programmer
and a recorder.

Thermogravimetry analysis (TGA)

 The plot of mass change in percentage versus
temperature or time (known as TGA curves or Thermogram)
is the typical result ofTGA analysis as shown in Figure below.

 There are two temperatures in the reaction:

 Ti (starting of decomposition temperature)

 lTofw(efsitntaelmtpeemratpuereraatturweh)icrheptrheeseonntsinegt the
of a
mass change is seen and the lowest
temperature at which the process has been
completed, respectively.

 sTthroenrgelaycdtieopnetnedmopnerthateucreonadnidtiionntserovfatlh(eTf -Ti) The plot of mass change with temperature.
experiments.

 Hence, they can not have any fixed values.

Thermogravimetric Curves

The thermogram is plot of change in weight verses temperature or

time. TG curve has following features

i) Horizontal portion AA1 indicates
the region where there is no

change in weight.

ie. The compound is stable up

to temp Ti
ii) The curve A1B1 indicates the

weight loss.

iii) Additional information that can

be obtained from a TG curve is

that how much weight is lost by

heating a sample at a given

temp.

Interpretation of TGA Curves

 TGA curves are typically
classified into seven types
according to their shapes.
Figure shows schematic
of various types ofTGA
cur ves.

Schematic of various types ofTGA curves.

Interpretation of TGA Curves

 Curve 1: No change:This curve
depicts no mass change over the
entire range of temperature,
indicating that the decomposition
temperature is greater than the
temperature range of the
instrument.

 Curve 2: Desorption / drying:
This curve shows that the mass
loss is large followed by mass
plateau. This is formed when
evaporation of volatile product(s)
during desorption, drying or
polymerization takes place. If a
non-interacting atmosphere is
present in the chamber, then curve
2 becomes curve 1.

Figure 3: Schematic of various types ofTGA curves.

Interpretation of TGA Curves

 Curve 3: Single stage
decomposition:This curve
is typical of single-stage
decomposition temperatures
having Ti and Tf.

 Curve 4: Multistage
decomposition: This curve
reveals the multi-stage
decomposition processes as a
result various reactions.

 Curve 5: Similar to 4, but
either due to fast heating rate
or due to no intermediates.

Figure 3: Schematic of various types ofTGA curves.

Interpretation of TGA Curves

 Curve 6:Atmospheric reaction:
This curve shows the increase in
mass.This may be due to the
reactions such as surface oxidation
reactions in the presence of an
interacting atmosphere.

 Curve 7: Similar to curve 6, but
product decomposes at high
temperatures. For example, the
reaction of surface oxidation
followed by decomposition of
reaction product(s).

Figure 3: Schematic of various types ofTGA curves.

Example 1 (Dehydration, Desorption) : Dehydration of CuSO4·5H2O

• e.g. dehydration of CuSO4·5H2O

TG curve for CuSO45H2O

Example 2 (Decompostion) :TGA Curve for AgNO3

• The horizontal portion of the curve indicates

that, there is no change in weight (AB &CD) and AgNO3
the portion BC indicates that there is weight

change.

• The weight of the substance (AgNO3) remains
constant up to a temperature of 473°C indicating

that AgNO3 is thermally stable up to a temperature Ag + NO2 + O2
of 473°C.

• At 473°C temperature it starts losing its weight

and this indicates that the decomposition starts

at this temperature. It decomposes to NO2, O2
and Ag.

• The loss in weight continues up to 608°C and The diagram indicates the TGA curve

beyond this temperature the weight of the sample for AgNO3.
remains constant, this is shown by the portion of

the curve CD. AgNO3 → Ag + NO2 + O2
• The portion between BC, represents the

decomposition of silver nitrate, the
decomposition is complete at 608°C leaving

metallic silver as the stable residue

Example 3 (Oxidation) : Oxidation of the P92 ferritic/martensitic

steel • TGA measurements of the mass change as a

5.97 mg/cm2 function of oxidation time of uncoated and

coated P92 steel (curves: a, b) are shown in

Figure. The samples were oxidized at 650 °C

in Ar+40% H2O atmosphere for 240 h.
• When the mass gain of the samples was

compared at about 240 h of oxidation, the

coated sample had gained a mass of about
0.0199 mg/cm2 0.0199 mg/cm2 (curve b), while uncoated

P92 steel had gained about 5.97 mg/cm2

(curve a).

Mass gain vs. Oxidation time of the P92 steel • These results indicated that the Al-Mn CVD-

without and with Al-Mn-CVD-FBR coating at 650 °C FBR coating increased the oxidation
in Ar+40%H2O: (a) P92 steel and (b) Al-Mn/P92 resistance of P92 steel up to 300 times,
sample. approximately.

CVD in a fluidized bed reactor (CVD-FBR)

Example 4 (Corrosion, Oxidation) : Effect of CeO2 on oxidation
behaviors of ferritic stainless steel with Ni-Fe coating. (in air at 800 °C)

• Mass changes of the bare steel and the coated
samples against oxidation time are presented in
Fig. (a). As shown in Fig. (b), the square of the
mass change is in a linear proportion to the
oxidation time, suggesting that the oxidation of all
the samples follows approximately a parabolic rate
law.

• Based on the graph, the parabolic rate constants
could be calculated to be 7.4 × 10−14, 7.8 × 10−14
and 2.4 × 10−14 g2 cm−4 s−1 for the bare, Ni-Fe and
NiFe-CeO2 coated samples, respectively.

• The Ni-Fe coating doesn't reduce the growth rate
of the oxides. However, the addition of CeO2 to the
coating improves obviously its oxidation
resistance.

Mass changes (a) of the bare and coated 430SS oxidized in air
at 800 °C and their parabolic plots (b).



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Differential Scanning
Calorimetry (DSC)

• A DSC measures the difference in
Heat Flow Rate between a sample and
inert reference as a function of time and
temperature.

• Differential Scanning Calorimetry
determines transition temperatures,
heat capacity, monitor reactions, and
determine kinetics of processes.

Differential Scanning Calorimetry (DSC)

• Calorimetry – (n) Measurement of the amount of heat evolved
(heat out) or absorbed (heat into) in a chemical reaction,
biological process, change of state or formation of a solution.

• A differential calorimeter measures the heat of a

sam p l e 1relative to a .refere nce.
• A differential scannin g calorim eter does all of the above

and heats/co ols the, sample with a linear/modulating
temperature ramp.

• Differential Thermal Analysis (DTA):

• Measures temperature difference (dT) between the sample and the
reference.

• Differential Scanning Calorimetry (DSC):

• Measures heat flow difference (dH/dT) between the sample and
the reference.
•

DTA and DSC

 DSC - A thermal technique in which the differences in heat
(energy or power) flow into/out a substance (sample) and a
reference (blank pan) are measured as a function of temperature
while the two are subjected to a controlled temperature
program (heating, cooling, etc.)

 DTA - A thermal technique in which the difference in
temperature between a substance (sample) and a reference
material (iner t such atsheAl2sOub3sptaonwcdeera)nids measured as a function of
temperature while reference material are
subjected to a controlled temperature program (heating, or
cooling at various different rates)

DTA: designed for temperature range up to 1500℃. (for metals and inorganic
materials).
DSC: limited to temperature range up to 750℃ (max). (for organics, polymers,
and low-melting metals)

Differential scanning calorimetry (DSC)

 DSC is a thermo-analytical technique in which the differences in the amount
of heat required to increase the temperature of a sample and
reference are measured as a function of temperature.

 Both the sample and reference are maintained at nearly the
same temperature throughout the experiment.

 The reference sample should have a well defined heat capacity over the range of
temperatures to be scanned and analyzed.

 In general, the temperature program of the DSC is designed to increase the sample
holder temperature linearly as a function of time.

 The main application of DSC is in studying phase transitions such as melting point,
glass transitions, or exothermic decompositions.

 These transitions involve energy changes or heat capacity changes that can be detected
by DSC with great sensitivity.

Instrumentation

 A DSC is a twin instrument, comprising of individual sample and reference calorimeters
within a common thermal enclosure, the cell.

Principle of Operation

 When a sample undergoes a physical transformation such as a
phase transition, more or less heat will need to flow to it
than to the reference (typically an empty sample pan) to
maintain both at the same temperature.

 Whether more or less heat must flow to the sample depends on
whether the process is exothermic or endothermic.

 For example, as a solid sample melts to a liquid it will require
more heat flowing to the sample to increase its temperature at
the same rate as the reference.

 This is due to the absorption of heat by the sample as it
undergoes the endothermic phase transition from solid to
liquid.

Principle of Operation

 Likewise, as the sample undergoes exothermic processes
(such as crystallization) less heat is required to raise the
sample temperature.

 By observing the difference in heat flow between the sample
and reference, differential scanning calorimeters are able to
measure the amount of heat absorbed or released during such
transitions.

 DSC may also be used to observe more fine/quick phase
changes, such as glass transitions.

Applications of DSC

 Determination of transition temperatures (Tg,Tm,Tc, etc.),
and the energies involved in the transitions.

 Heat of fusion, extents of crystallization, etc.
 Glass transition and melting temperatures.

 Kinetics studies (isothermal experiments）

 Crystallinity and crystallization rates
 Reaction kinetics

 Determination of purity in compounds – by measuringTm

Typical DSC curve

Information about the DSC curves

 In general, the result of a DSC experiment is a curve of heat
flux versus temperature or versus time.

 This curve can be used to calculate enthalpies of transitions,
i.e., ΔH = kA

(where, H is the enthalpy of transition, k is the calorimetric
constant, and A is the area under the curve) , which is done by
integrating the peak corresponding to a given transition.

 The value of k is typically given by the manufacturer
for an instrument or can generally be determined by
analyzing a well- characterized sample with known
enthalpies of transition.

Evaluation and interpretation of DSC curves

 Figure shows the typical DSC curve for a sample exhibiting
endotherm of melting at a particular heating rate.

 The onset of melting (122.8°C) and peak temperature of
melting (123.66°C) can be determined by extrapolation
technique and peak values, respectively.

 The enthalpy change can be calculated by integrating the
area under the curve.The unit can be either J/g or
J/mole depending on the nature of the sample.

DSC curve of a sample.

Effect of heating rate:

 Heating rate affects the melting point and enthalpy of melting. Figure
shows the typical DSC curves taken at different heating rate.

 With increasing heating rate, the onset of the melting does not
change significantly, but the peak point of melting shifts slowly
to higher temperature.

Typical DSC curves taken at different heating rates.

Effect of sample weight

 The sample weight also affects the thermal properties
significantly. Figure shows the typical DSC curves taken at a
constant heating rate for different mass of the samples.

 It could be clearly seen that the onset of melting, peak point
of melting and enthalpy undergo small variations when
the sample mass is changed.

Typical DSC curves taken for different weighed
samples

Example 1 (transition temperatures) : Transformation temperatures of a
shape memory alloy (Cu-Al-Ni alloy ) determined by DSC Analysis

• Cu-Al-Ni alloy shape memory material undergoes
a martensite to austenite transformation upon
heating.

• The lower curve of the DSC plot in the figure
below shows the endotherm which results when
the sample was heated at a rate of 5°C/min. from
30°C to 190°C in nitrogen gas flowing at a rate of
25ml/min.

• Upon cooling down, the austenite to martensite
transformation yields an exotherm seen in the
upper trace of the DSC plot.

• There is a hysteresis in the transformation on
heating and cooling which is notable. The on-set
temperatures, 145.06°C on heating and 145.88°C
on cooling are close

Example 2 (Melting point, purity): Melting Point Determination on
Palladium

• The DSC curve (blue) shows the
melting with an enthalpy of 158 J/g
(blue curve, DSC) at 1554°C (onset
temperature). Both values correspond
very well with literature data (< 1%) for
pure Pd.

• Before and after melting no mass loss
occurred (green curve); this confirms
the high purity of the metal as well as
the vacuum-tightness of the
equipment.

Example 3 : Effect Heating Rate of Au70Cu5.5Ag7.5Si17

(a) DSC heat flow curves normalized to the heating rate.
At low rates, a glass transition (Tg), exothermic
phase transition peaks (T1 and T2) and endothermic
melting (Tm) can be seen. The phase transition
temperatures T1 and T2 shift to higher temperatures
with increasing heating rate, and at sufficiently high
rates an unexpected endothermic peak (at Te) arises
after T1 and just before T2.

(b) Close-up of second exothermic peak (T2). The onset
of T2 peak shifts to higher temperatures with
increasing rates and changes its shape and size if
located above Te.

Example 4 : Dehydration of CuSO4·5H2O

Corresponding TG curve

48

THERMAL ANALYSIS

Dynamic Mechanical
Analysis (DMA)

A technique in which the sample's kinetic
properties are analyzed by measuring
the strain or stress that is generated
as a result of strain or stress, varies
(oscillate) with time, applied to the
sample.

Dynamic mechanical analysis

Dynamic mechanical analysis (DMA) is a technique used to study and
characterize materials. It is most useful for studying the viscoelastic
behavior of materials. A sinusoidal stress is applied and the strain in the
material is measured, allowing one to determine the modulus.
• The temperature of the sample or the frequency of the stress or time

or atmosphere are often varied, leading to variations in the modulus.
• This approach can be used to locate the glass transition temperature

of the material.

A typical DMA tester with grips to hold sample and environmental chamber to
provide different temperature conditions. A sample is mounted on the grips and the
environmental chamber can slide over to enclose the sample.