tga decomposition kinetics - .tga decomposition kinetics 78 decomposition kinetics background...
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TGA
Decomposition Kinetics
78
Decomposition Kinetics Background
Includes isothermal and constant heating rate methods.
Constant heating rate method is the fastest and will be discussed here.
Based on method of Flynn and Wall Polymer Letters, 19, 323, (1966).
Requires collection of multiple curves at multiple heating rates.
Ultimate benefit obtained in Life-Time plots.
89
79
TA Specialty Library -- TGA Kinetics
Requires at least 3 TGA runs at different heating rates or 1 Modulated
TGA run
Calculates Activation energy & conversion curves
Ultimate benefit is predictive curves Lifetime Plots
80
Kinetic Analysis
The rate at which a kinetic process proceeds depends not only
on the temperature the specimen is at, but also the time it has
spent at that temperature.
Typically kinetic analysis is concerned with obtaining
parameters such as activation energy (Ea), reaction order (k),
etc. and/or with generating predictive curves.
90
81
Kinetic Analysis, cont.
Activation energy (Ea) can be defined as the minimum
amount of energy needed to initiate a chemical process.
State 1
State 2
Ea
With Modulated TGA, Ea can be
measured directly.
82
TGA Kinetics - Wire Insulation Thermal Stability
91
83
TGA Kinetics - Heating Rate vs. Temperature
1.4 1.5 1.6
1
2
5
10
1000/T (K)
Ln (
HE
AT
RA
TE
) (
C/m
in)
460 440 420 400 380 360
20 10 5
2.5 1.0 0.5
Conversion
Activation Energy (Ea) Slope
84
TGA Kinetics - Estimated Lifetime
TEMPERATURE (C)
1.5 1.6 1.7 1.8 1.9 10
100
1000
10000
100000
1000000
1000/T (K)
ES
TIM
AT
ED
LIF
E (
hr.
)
260 280 300 320 340 360
1 century
1 decade
1 yr.
1 mo.
1 week
1 day
ES
TIM
AT
ED
LIF
E
92
Thermogravimetry Under Extreme
High Heating Rate Conditions
What Constitutes Extreme Conditions?
High Heating Rates
Kinetic Studies
Sample Throughput
93
Rapid Heating Thermal Analysis
Gasification, combustion, and volatilization are complex
processes.
Thermal treatments by different heating rates and
time/temperature relationships can result is different
chemical decomposition products.
As an example, heating at a high rate can result in the
thermal degradation of component that would otherwise
volatilize at a slow heating rate.
Rapid heating rates, as on the TA Instruments Discovery
TGA and pyrolysis GC/MS, provide powerful techniques
to investigate the time/temperature relationships
Discovery TGA & Q5000 IR Innovative IR-Heating Furnace
94
DTGA Ballistic Heating Performance
0
500
1000
1500
2000
[
] D
eriv
. Tem
pera
ture
(C
/min
)
0
200
400
600
800
Tem
pera
ture
(C
)
0 2 4 6 8
Time (min)
Run #1Run #2Run #3Run #4
Equilibrate method
segment is very
repeatable and achieves
rates approaching
2000C/min in this application
DTGA Heating Rate Comparison-
Temperature
20C/min
500C/min
95
DTGA Heating Rate Comparison-Time
20C/min
500C/min
High Heating Rate TGA: Kinetic
Studies
96
Effect of Heating Rate on Decomposition
Temperature of Polystyrene
0
20
40
60
80
100W
eig
ht (%
)
0 100 200 300 400 500 600
Temperature (C)
Polystyrene 20C/minPolystyrene 10C/minPolystyrene 5C/minPolystyrene 1C/min
Universal V4.2D TA Instruments
TGA: Copier Paper in Air
0.5 to 50 C/min =======>
BREAK
PLATEAU
RESIDUE
0
20
40
60
80
100
Weig
ht (%
)
0 200 400 600 800 1000
Temperature (C) Universal V4.4A TA Instruments
97
TGA: Quantitation of Copier Paper
HEATING BREAK PLATEAU RESIDUE
RATE weight % weight % weight %
__C/min__ __________ __________ __________
0.5 40.63 16.32 9.87
1 41.09 16.64 9.85
2.3 41.27 16.70 -
5 41.55 16.66 9.79
10 41.82 16.57 9.74
23 41.40 16.63 9.90
50 40.35 16.70 9.88
100 37.67 17.06 10.08
230 33.53 16.68 9.83
500 31.46 - 9.77
- - - -
Equilibrate 25.06 - 9.66
> 2300 C/min
Average 41.29 16.66 9.84
STD DEV 0.41 0.19 0.11
TGA: Semi-Log Plot of Copier Paper
0.5 C/min
5.0 C/min
50 C/min
500 C/min
Equilibrate>2000 C/min
6 Seconds 10 Minutes 16.7 Hours
0
20
40
60
80
100
Weig
ht (%
)
0
20
40
60
80
100
Weig
ht (%
)
0.01 0.1 1 10 100 1000 10000
Time (min) Universal V4.4A TA Instruments
*
* No data at 1000 C/min
98
TGA: High Heating Rates of Copier Paper
EQUILIBRATE> 2300 C/min
EQUILIBRATE> 2300 C/min
500 C/min
230 C/min
BUNCHING 50 of 500 C/min
0.5 C/min
5.0 C/min
0
20
40
60
80
100
Weig
ht (%
)
200 400 600 800
Temperature (C) Universal V4.4A TA Instruments
Modulated TGA Technology
A New Approach for
Obtaining Kinetic Parameters
99
Temperature Change in MDSC and MTGA
MTGA OF 60% EVA WITH LINEAR RAMP
150 200 250 300 350 400 450 500
-20
0
20
40
60
80
100
120
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
Temperature ()
We
igh
t (%
)
[---
----
----
-] D
eri
v. M
od
ula
ted
We
igh
t (%
/min
) TGA Modulated
100
GENERAL THEORY OF MTGA
ARRHENIUS AND GENERAL RATE
EQUATIONS
101
KINETIC EXPRESSION RATIO
FACTOR JUMP EQUATION AT
CONSTANT CONVERSION
102
FOURIER TRANSFORMATION YIELDS
MODULATED TGA EQUATION
103
FIRST ORDER PRE-EXPONENTIAL
FACTOR
FAST FOURIER TRANSFORMATION
Fast Fourier Transformation yields
continuous kinetic parameters
104
LINEAR HEATING PROFILE FOR
POLYTETRAFLUOROETHYLENE
TGA: MTGA - Activation Energy for
Polytetrafluoroethylene
400 450 500 550 600
0
200
400
600
800
1,000
-10
10
30
50
70
90
110
Temperature ()
Ac
tiva
tio
n E
ne
rgy (
kJ
/mo
l)
[
] W
eig
ht
(%)
105
EVA(60%Vac)
EFFECT OF CONVERSION ON
ACTIVATION ENERGY
106
QUASI-ISOTHERMAL MTGA OF PTFE
QUASI-ISOTHERMAL MTGA OF PS
107
MTGA OF 60% EVA WITH DYNAMIC
HEATING RATE
MTGA REPEATABILITY
POLY (60% ETHYLENE VINYL ACETATE)
108
MTGA KINETICS COMPARISON
MTGA EXPERIMENTAL CONDITIONS
Period : > 200 seconds
(temperature range dependent)
Amplitude : 4 - 5 C
Cycles Across Transition : > 5
Temperature Program
Isothermal or
Heating Rate : < 2 C/min
109
DETERMINATION OF FULL WIDTH
TEMPERATURE AT HALF HEIGHT
BENEFITS OF MTGA METHOD
SINGLE EXPERIMENT
INCREASED PRODUCTIVITY
MODELFREE
EASY OF USE
OBTAIN Z WITH ASSUMPTION OF 1st ORDER MODEL
COMPLETE KINETIC INFORMATION
E & Z AS A FUNCTION OF CONVERSION
FOLLOW PROCESS CHANGES
110
Evolved Gas Analysis
122
Why Use Evolved Gas Analysis?
TGA measures weight changes (quantitative)
Difficult to separate, identify, and quantify individual degradation products (off-gases)
Direct coupling to identification techniques (Mass Spec, FTIR) reduces this problem
111
123
TGA-EGA: Typical Applications
Polymers (composition, hazard evaluation, identification)
Natural Products (contamination in soil, raw material selection {coal, clays})
Catalysts (product/by-product analysis, conversion efficiency)
Inorganics (reaction elucidation, stoichiometry, pyrotechnics)
Pharmaceuticals (stability, residual solvent, formulation)
124
Q50/Q500 EGA Furnace Sche