Introduction to Thermal Analysis Methods
• Definition:
Thermal analysis refers to a variety of techniques in which physical property of a
sample is continuously measured as a function of temperature, whist the sample is
subjected to a predetermined temperature profile.
• Where is Thermal Analysis used?
• Thermal Analysis techniques are used in virtually every area of modern
science and technology. The basic information that these techniques provide,
such as crystallinity, specific heat and expansion, are relied on heavily for the
research and development of new products. Thermal Analysis techniques also
find increasing use in the area of quality control and assurance, where
demanding requirements must be met in an increasingly competitive world.
And of course thermal analysis instruments are used in universities for
applications ranging from basic undergraduate studies to the most
sophisticated postgraduate research.
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Introduction to Thermal Analysis Methods
HKUST
Introduction to Thermal Analysis Methods
HKUST
• Definition:
Thermal analysis refers to a variety of techniques in which physical property of a
sample is continuously measured as a function of temperature, whist the sample is
subjected to a predetermined temperature profile.
• Where is Thermal Analysis used?
• Thermal Analysis techniques are used in virtually every area of modern
science and technology. The basic information that these techniques provide,
such as crystallinity, specific heat and expansion, are relied on heavily for the
research and development of new products. Thermal Analysis techniques also
find increasing use in the area of quality control and assurance, where
demanding requirements must be met in an increasingly competitive world.
And of course thermal analysis instruments are used in universities for
applications ranging from basic undergraduate studies to the most
sophisticated postgraduate research.
Introduction to Thermal Analysis Methods
HKUST
• Major Techniques:
– Thermal Gravimetric Analysis (TGA)
– Differential Thermal Analysis (DTA)
– Differential Scanning Calorimetry (DSC)
– Dynamic Mechanical Analysis (DMA)
– Thermomechanical Analysis (TMA)
• Other techniques:
– Melt Elasticity Index
– Dielectric Analysis
– Thermally Stimulated
Current/Relaxation Map Analysis
– Free Volume Microprobe
– Differential Photo Calorimetry
– Thermal Conductivity Analysis
Introduction to Thermal Analysis Methods
HKUST
TG or TGAThermal Gravimetric Analysis
TGA examines the process of weight
changes as a function of time, temperature,
and other environment conditions that may
be created within the apparatus.
Heating Temperature Rate
Sample Weight Change
Atmosphere
Introduction to Thermal Analysis Methods
HKUST
Typical TGA curve
W
e
i
g
h
t
L
o
s
s
(
w
t
.
%
)
1
s
t
D
e
r
i
v
a
t
i
v
e
(
m
g
/
m
i
n
x
1
0

2
)
100 200 300 400 500
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
0.0
Temperature (ºC)
Ti Te Td
∆W
2.0
2.0
4.0
6.0
8.0
10.0
Introduction to Thermal Analysis Methods
HKUST
∗ Effect of Atmosphere on Mass
Buoyancy: the change in density of the gas phase with temperature.
ρair ↓ ⇒Wspecimen↓
example:
ρdry air =1.3 mg/cm3 , 25 oC
ρdry air =0.3 mg/cm3 , 1000 oC
For : 20 mg Sample ( ρ =1.0g/ cm3 )
25 oC → 1000 oC
A 0.1 wt% loss will be introduced due to Buoyancy
Introduction to Thermal Analysis Methods
HKUST
TABLE
MAJOR FACTORS AFFECTING THERMOGRAVIMETRY
Mass Temperature
Buoyancy Heating rate
Atmospheric turbulence Thermal conductivity
Condensation and reaction Enthalpy of the process
Electrostatic and magnetic forces Sample, furnace, and sensor arrangement
Electronic drift Electronic drift
Introduction to Thermal Analysis Methods
HKUST
• The range of materials can be studied by
thermal analysis
– Biological materials
– Building materials
– Catalysis
– Ceramics and Glasses
Applications of TGA:
Composition
Moisture content
Solvent content
Additives
Polymer content
Filler content
Dehydration
Decarboxylation
Oxidation
Decomposition
Dm = mass change
dm/dt = rate of mass change/decomposition
DTG = derivative thermogravimetry
DTG Peak = characteristic decomposition
temperatures ® identification
Tonset = thermal stability
Introduction to Thermal Analysis Methods
HKUST
Example of using TGA to identify the composition of a PP/PE blend
Introduction to Thermal Analysis Methods
HKUST
(1) Additives
Oxidation → Weight gain → Temperature ~ time →
Anti Oxidation additive concentration
(2) Extent of Cure
Residual Weight loss → Degree of cure
(3) Thermal Stability
(4) Reactivity & Phase Equilibration in Ceramics
Introduction to Thermal Analysis Methods
HKUST
TGA Curve  I
Introduction to Thermal Analysis Methods
HKUST
Introduction to Thermal Analysis Methods
HKUST
Effect of Sulfonation Treatment
⇓
Degree of Stability
Introduction to Thermal Analysis Methods
HKUST
Introduction to Thermal Analysis Methods
HKUST
Introduction to Thermal Analysis Methods
HKUST
DSC
Introduction to Thermal Analysis Methods
HKUST
DSC and DTA are techniques by which 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.
Applications:
•characteristic temperatures identification
•glass transitions
•melting and crystallization behavior
•heat of melting and crystallization
•purity
•compatibility
•polymorphism
•solidliquid ratio
•specific heat capacity
•reaction behavior
•heat of reaction
•reaction kinetics
•oxidative stability
•thermal stability
Differential Thermal Analysis (DTA)
Differential Scanning Calorimetry (DSC)
Introduction to Thermal Analysis Methods
HKUST
Typical DSC curve
H
e
a
t
F
l
o
w
(
m
W
)
50 100 150 200 250 300
20
15
10
5
0
5
10
15
Tonset TC
Tp
Exo
Temperature (ºC)
25
Introduction to Thermal Analysis Methods
HKUST
Measurement of Glass Transition Temperature
(Tg) by DSC and Rate Effects
Tg measurement by DSC
Introduction to Thermal Analysis Methods
HKUST
TABLE VIII
EVENTS DETECTED BY DTA AND DSC AND THEIR EFFECTS DURING EATINGH
Transformation Observation Reaction Observation
Firstorder Endothermic Liquidsolid Either
Higherorder Step in base Homogeneous Either
Lambda Endothermic Polymerization Exothermic
Metastable to stable Exothermic Gascondensed phase Either
Introduction to Thermal Analysis Methods
HKUST
Introduction to Thermal Analysis Methods
HKUST
Typical DTA and DSC
curves for the melting of
ice, illustrating several
methods of defining the
baseline. Relative error of
the enthalpy due to each
baseline construction is
given relative to an
exponential function taken
as the “true” baseline.
Introduction to Thermal Analysis Methods
HKUST
Typical DTA and DSC curves illustrating several
methods of defining the baseline
Introduction to Thermal Analysis Methods
HKUST
Introduction to Thermal Analysis Methods
HKUST
Representations of two heatflux
calorimeters showing
(a) the Boersma therr Couple placement
(b) the TianCalvet design
(c) The schematic diagram is
appropriate.
Introduction to Thermal Analysis Methods
HKUST
General principles and schematic for a DTA apparatus
Introduction to Thermal Analysis Methods
HKUST
(1) Solid State Transitions
(2) Solid State Reactions
(3) Solid State Decompositions
Applications of DTA & DSC
(A) Crystallinity
DSC can determine the presence & concentration of a crystalline phase in a
solid, as well as the melting point of the crystals.
(B) The Glass Transition, Tg
DSC can detect the glass transition of an amorphous materials, such as
polymer.
(C) Characterization of Alloys & Composites
(D) Aging and Degradation
(E) Phase Diagram of alloys
Introduction to Thermal Analysis Methods
HKUST
Differential Scanning calorimetry (DSC)
Samuel S. KIM
Differential scanning calorimetry (DSC) is one of the most useful techniques applicable to the
assessment of enthalpy changes that accompany various material transformations. DSC
measures, for example, the endothermic steplike change in heat flow rate that occurs at the glass
transition temperature (Tg). It can identify and characterize polymerization, cross linking,
crystallization, and fusion ( or melting) of crystallites in terms of heat evolved or absorbed and
the associated transition temperatures. Furthermore, these thermal data enable one to deduce the
reaction rate constant, kinetic reaction order, activation energy, etc. DSC analyses can be made
either isothermally as a function of time of dynamically as function of temperature.
DSC is particularly suited to the characterization of mold compounds. For example, DSC enables
one to assess how fast the mold compound is curing at the transfer molding temperature and to
measure the effect of a particular catalyst on the cure rate, the initial asmolded Tg, and the final
postcured Tg.
Experimental procedures for DSC are rather simple. For analysis by DSC, a 520 mg sample
of a solid is placed in a small Al pan, which is subsequently covered with an Al lid and tightly
crimped around the edge. It is then transferred into the DSC cell and cured either isothermally or
dynamically, depending on the desred cure mode. In the case of a volatile or liquid sample, a
highpressure steel sample cup is available for hermetic sealing.
Introduction to Thermal Analysis Methods
HKUST
Figure 2.20 is a typical dynamic DSC thermo gram. In the beginning of the thermal
scanning, an increase in the observed heat flow is due to the thermal stabilization of the
instrument and the specimen. The first sharp peak is an endothermic characteristic
representing the T g of uncured starting material. The second peak, denoted by A, is due to
exothermic hear liberated during the cure reaction. From a series of dynamic scans of samples
cured isothermally at a given temperature for different times one can monitor the progressive
change in T g as well as the degree of cure. In parallel with this, multiple isothermal analyses
at different temperatures enable one to evaluate various reaction kinetic parameters.
The reaction rate is given by the following equation:
Rate =dα/dt =kf(α) (1)
Where α is the degree of conversion or cure, k is the rate constant, and f(α) is some function
of the reactive group conversion. The reaction rate constant, k, in turn, is expressed in the form
of Arrhenius equation.
k= AE/RT (2)
Where A is the frequency factor, E is the activation energy, R is the gas constant, and T is the
absolute temperature. Combining Equations 1 and 2 and taking the logarithm of both sides one
obtains
ln(dα/dt )=ln[Af(α )] – E/RT (3)
Introduction to Thermal Analysis Methods
HKUST
In DSC measurements, the degree of cure of conversion can be estimated from the ratio of
the amount of heat evolved for the partial conversion after time t at a given temperature, Ht , to
the total heat evolved for the complete conversion, H 0 :
α = Ht / H0 (4)
The rate Equations 1 and 3 can be rewritten as
dα/dt = (1/ H0)(d Ht/dt) (5)
ln(dα/dt ) = ln [(1/ H0)(d Ht/dt)]= ln[Af(a)]E/RT (6)
If f(α) is a function of conversion but not of temperature, the activation energy, E, can be
obtained by plotting ln [(1/ H0)(d Ht/dt)] versus 1/T at a fixed conversion. From Equation 6 one
can see that E can be calculated from the slope of the line.
It is also generally assumed that f (α) can be expressed in terms of both α and the reaction
kinetic order, n, as follows:
f(α) = (1 α)n (7)
The rate Equation 6 then can be rewritten in combination with Equation 7 as
ln(dα/dt ) = lnAE/RT + nln(1a) (8)
Introduction to Thermal Analysis Methods
HKUST
One can see from Equation 8 that a plot of ln(rate) versus ln(1α) should provide a
straight line for isothermal runs at a given temperature at various conversions, The slope of
the line should yield the kinetic reaction order, n.
With the use of this formalism and a series of isothermal experiments, as shown in Figure
2.20, the kinetic order and the activation energy were calculated to be 1.41 and
107.1kJ/mole, respectively, for the mold compounds, which consist of a diglycidyl ether of
bisphenol A type and phenolic resin.
References:
1. C.C.Riccardi, H.E.Adabbo, and J.J.Williams. J.Appl.Polym.Sci. 29. 2481, 1984
2. V.M.Gonzalez and N.Casillas. Polym.Eng. and Sci. 29, 295, 1989
3. H.E.Kissinger. Anal. Chem.29, 1702, 1957
4. Internal technical report. Rohm and Haas Co., May 1989.
Introduction to Thermal Analysis Methods
HKUST