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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

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