thermogravimetric analysis theory, operation, calibration and data interpretation
DESCRIPTION
Thermogravimetric Analysis Theory, Operation, Calibration and Data Interpretation. Prepared by Kadine Mohomed, Ph.D Thermal Applications Chemist TA Instruments. Agenda: TGA Theory, Operation and Calibration. Definitions and review of instrument Balance, furnace and heat exchanger review - PowerPoint PPT PresentationTRANSCRIPT
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Thermogravimetric AnalysisTheory, Operation, Calibration and Data
Interpretation
Prepared by Kadine Mohomed, Ph.D
Thermal Applications Chemist
TA Instruments
12.57% Water(0.8753mg)
19.47% Carbon Monoxide(1.355mg)
30.07% Carbon Dioxide(2.093mg)
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Sample: calcium oxalateSize: 6.9610 mgMethod: Ramp
TGAFile: 111301.001Operator: cgsRun Date: 13-Nov-01 10:16Instrument: TGA Q50 V2.34 Build 127
Universal V3.4A TA Instruments
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Agenda: TGA Theory, Operation and Calibration
• Definitions and review of instrument
• Balance, furnace and heat exchanger review
• Mass and temperature calibration
• Purge gas considerations
• Baseline considerations
• Sample preparation and pan selection
• Method development
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TGA: The Technique
Thermogravimetric Analysis (TGA) measures the amount and rate of change in the weight of a material as a function of temperature or time in a controlled atmosphere.
Measurements are used primarily to determine the composition of materials and to predict their thermal stability at temperatures up to 1000°C. The technique can characterize materials that exhibit weight loss or gain due to decomposition, oxidation, or dehydration.
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What TGA Can Tell You
•Thermal Stability of Materials•Oxidative Stability of Materials•Composition of Multi-component Systems•Estimated Lifetime of a Product•Decomposition Kinetics of Materials•The Effect of Reactive or Corrosive Atmospheres
on Materials•Moisture and Volatiles Content of Materials
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Calcium Oxalate Example
12.57% Water(0.8753mg)
19.47% Carbon Monoxide(1.355mg)
30.07% Carbon Dioxide(2.093mg)
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Sample: calcium oxalateSize: 6.9610 mgMethod: Ramp
TGAFile: 111301.001Operator: cgsRun Date: 13-Nov-01 10:16Instrument: TGA Q50 V2.34 Build 127
Universal V3.4A TA Instruments
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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.
• Weight Gain:– Oxidation: Interaction of the sample with an oxidizing
atmosphere.– Absorption.All of these are kinetic processes (i.e. there is a rate at
which they occur).
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Features of the Q500/ Q50 TGA
The Q500 is a research grade thermogravimetric analyzer, whose leading performance arises from a responsive low-mass furnace; sensitive thermobalance, and efficient horizontal purge gas system (with mass flow control). Its convenience, expandability and powerful, results-oriented software make the Q500 perfect for the multi-user laboratory where a wide variety of TGA applications are conducted and where future expansion of analytical work is anticipated.
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Photodiodes
Infrared LED Meter movement
Balance arm
Tare pan
Sample platform
Thermocouple
Sample pan Furnace assembly
Purge gas outlet
Heater
Elevator base
Purge gas inlet
Sample pan holder
1. Q Series Two Point Mass Adjustment•200mg range •1000mg. range
*No need to do a mass recalibrationwhen switching from regular Pt pans toPt pans with Al hermetic pans. *Mass Loss Reference MaterialsMaterials with nominal 2%, 50% and 98%
mass loss are available for verification of TGA
weight calibration.
2. Curie Point Transition Temperature Calibration
•ASTM 1582 *Curie Temperature Reference Materials:TA Instruments is the exclusive worldwide
distributor for a set of six certified and traceable
Curie temperature materials developed by ICTAC
Features of the Q500 TGA
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Q50/Q500 Features and Options
Feature Q500 Q50
Furnace – low mass Standard Standard
Furnace – EGA Option Option
Temperature Range RT-1000°C RT-1000°C
MFC / GSA Standard Option
Autosampler Option NA
Hi-Res TGA™ Option NA
Modulated™ TGA Option NA
Touch-screen display Standard NA
TGA / MS operation Option Option
TGA / FTIR operation 3rd Party 3rd Party
NA = Not Available
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TGA Furnaces
• Standard Furnace
– Low mass
– Used for Hi-Res Runs
– Cools down in <20min
• EGA Furnace
– Higher Mass
– Used for EGA runs due to quartz liner
– Cools down in ~40min
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TGA: Purge Gas Flow
60ml/min
90ml/min
10ml/min40ml/min
Standard Furnace
EGA Furnace
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Standard Furnace
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EGA Furnace Schematic
Quartz Liner
Off-Gases
Balance Purge
Sample Thermocouple
SamplePan
Furnace Core
Purge Gas InLow internal
Volume ~15ml
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TGA: How the balance works
The balance operates on a null-balance principle. At the zero, or “null” position equal amounts of light shine on the 2 photodiodes.
If the balance moves out of the null position an unequal amount of light shines on the 2 photodiodes. Current is then applied to the meter movement to return the balance to the null position.
The amount of current applied is proportional to the weight loss or gain.
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TGA: Q Series MFC and GSA
MFC and GSA standard on Q500 and optional on Q50
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TGA: Q-Series Purge Gas Plumbing
• Instruments w/o MFC
– The gas 1 port purges the sample area only.
– The gas 2 port purges the balance area only.
• Instruments w/ MFC
– The gas 1 port purges both sample and balance areas.
– The gas 2 port is used when a different purge gas is required or gas switching is used.
– Selection of gas on NOTES page is critical for proper use of MFC calibration tables.
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Heat Exchanger – Cleaning
• Check cleanliness (no algae growth) once every 3-6 months.
• To clean dump old water, fill with new and add conditioner (algae growth suppressor) if available.
• For Q series, after filling, in software choose “Control \ Prime Exchanger”.
• For 2xxx, after filling, continue starting a dummy run until error 119 (heat exchanger – no flow) goes away.
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TGA Performance Criteria
• Baseline
– Drift Affected by TGA construction, balance quality, and
buoyancy effect (minimized through proper construction techniques and purge gas control)
• Sensitivity
– Affected by TGA balance quality
• Reproducibility
– Affected by balance quality, temperature control, and construction quality
• Temperature Accuracy
– Affected by thermocouple placement, calibration stability, purge gas interaction
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TGA Performance
• TGA Performance is primarily a function of balance sensitivity and baseline stability
• Balance sensitivity is optimized through design and construction techniques
• Baseline stability is a function of instrument design, as well as purge gas control
• TGA resolution is primarily a function of heating rate, but can be optimized using Hi-Res TGA
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Quantifying TGA Baseline Performance
Temperature or Time
Un
nor
mai
lzed
Sam
ple
Mas
s
Drift
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19.24µg
-5
0
5
10
15
20W
eig
ht
(µg
)
0 200 400 600 800 1000
Temperature (°C)
Sample: Empty PanSize: 0.0030 mgMethod: Dynamic Drift.001
TGAFile: O:...\0801-1000\0500-0872\dyndft.001
Run Date: 11-Aug-2006 08:52Instrument: TGA Q500 V20.1 Build 21
Measuring Q500 TGA Baseline Performance
Q500, 20°C/min Ramp
Drift ~19 g
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TGA: Calibrations
• Mass (Verify monthly)
• Temperature (Verify monthly)
• Platform (Perform if there is a problem picking up pans.)
Q series instruments w/ MFC will also have options to calibrate the sample and balance MFC’s. These have been calibrated by TA Instruments and should not require further calibration. Contact TAI if a problem arises.
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TGA: Mass Calibration
Two point mass adjustment: 2050, 2950, Q50, Q500 •100mg. (2XXX modules) or 200mg (Q series) range (use 100mg. weight)
•1000mg. range (use 1000mg. weight)
•Q5000IR – 100mg
•Run TGA weight calibration routine
•Follow screen instructions to tare and masscalibrate using two calibration weights (if known,enter exact mass of calibration weights)
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Mass Loss And Residue Validation
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We
igh
t (%
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0 50 100 150 200 250 300 350 400Temperature (°C)
2.4 %
49.7 %
99.1 %
0.017%
Mass Loss Reference Materials: Materials with nominal 2%, 50% and 98% mass loss are available for verification of TGA weight calibration.
P/N 952540.901 TGA / SDT Mass Loss Reference Materials Kit $1,760
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• Paramagnetic - a material that is susceptible to attraction by a magnet
• Curie Point Temperature - that temperature where the material loses its magnetic susceptibility (defined as offset point)
• Requires a magnet and well characterized transition materials
• ASTM 1582 - Standard Practice for Calibration of Temperature Scale for Thermogravimetry
Temperature Calibration: Curie Point Transition
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TGA: Temperature Calibration
Magnet
Vertical Balance Configuration - TGA 2050/2950/Q50/Q500
Sample
Tare
Furnace
Attraction of Sample to MagnetResults in Initial Weight Gain
%
temp
Offset
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TGA: Temperature Calibration Important Points
• Clear the ‘Temperature Table’ before performing the calibration runs (TGA only).
• Choose method end condition of “Furnace Closed”. This prevents the potential of the furnace opening onto the magnet at the end of the run and damaging the TGA.
• Start run and then put magnet under furnace. This allows capture of the weight increase (decrease) at the beginning.
• Use of a small labjack is recommended for holding the magnet in place under the furnace.
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Standards Can Be Run Simultaneously
99.5
100.0
100.5
101.0
101.5
We
igh
t (%
)
0 100 200 300 400 500
Temperature (°C)
Sample: alumel & nickelSize: 46.5600 mg
Comment: RT->450
TGAOperator: cgsRun Date: 14-Jun-01 16:23Instrument: AutoTGA 2950HR V5.4A
Alumel 157.00C
Nickel 368.80C
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Calcium Oxalate “Standard” Analysis
• Although Calcium Oxalate is not generally accepted as a “Standard Material,” it does have practical utility for INTRA-laboratory use
• Carefully control the experimental conditions; i.e. pan type, purge gases/flowrates, heating rate
• Particularly control the amount (~5mg) and the particle size of the sample and how you position it in the pan
• Perform multiple runs, enough to do a statistical analysis
• Analyze the weight changes and peak temperatures and establish the performance of YOU and YOUR instrument
• When performance issues come up, repeat the Calcium Oxalate analysis
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Calcium Oxalate Decomposition
• 1st Step CaC2O4•H2O (s) CaC2O4 (s) + H2O
(g)Calcium Oxalate Monohydrate Calcium Oxalate
• 2nd Step CaC2O4 (s) CaCO3 (s) + CO (g) Calcium Oxalate Calcium Carbonate
• 3rd Step CaCO3 (s) CaO (s) + CO2 (g)Calcium Carbonate Calcium Oxide
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0.0
0.6
[ ––
––
––
– ]
De
riv.
We
igh
t (%
/°C
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20
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60
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We
igh
t (%
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Temperature (°C)
Calcium Oxalate Repeatability
Overlay of 8 runs, same conditions
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Calcium Oxalate Repeatability
Transition 1 Transition 2 Transition 3Wt Change Peak Temp Wt Change Peak Temp Wt Change Peak Temp
Run # % °C % °C % °C1 12.13 156.68 18.78 493.37 29.62 684.332 12.22 153.60 18.75 494.17 29.56 680.433 12.20 155.40 18.76 495.6 29.63 684.114 12.21 155.58 18.77 495.98 29.69 688.115 12.21 154.05 18.75 494.72 29.54 684.286 12.20 154.91 18.73 495.62 29.58 684.837 12.21 155.09 18.77 494.71 29.61 683.928 12.20 153.52 18.77 493.84 29.57 681.85
Ave 12.20 154.85 18.76 494.75 29.60 683.98Std Dev 0.028 1.08 0.016 0.93 0.048 2.24
Theoretical 12.3 19.2 30.1Accuracy 0.8% 2.3% 1.7%Precision 0.2% 0.1% 0.2%
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General Considerations(Experimental Effects)
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TGA Curves are not ‘Fingerprint’ Curves
• Pan material type, shape and size.
• Ramp rate.
• Purge gas.
• Sample mass, volume/form and morphology.
Because most events that occur in a TGA are kinetic in nature (meaning they are dependent on absolute
temperature and time spent at that temperature), any experimental parameter that can effect the reaction rate
will change the shape / transition temperatures of the curve. These things include:
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Effect of Sample Size on Decomposition Temperature
0
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40
60
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100
We
igh
t (%
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Temperature (°C)
Polystyrene 17.6 mgPolystyrene 10.2 mgPolystyrene 5.4 mgPolystyrene 2.7 mg
Universal V4.2D TA Instruments
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Effect of Heating Rate on Decomposition Temperature
0
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40
60
80
100
We
igh
t (%
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0 100 200 300 400 500 600
Temperature (°C)
Polystyrene 20°C/minPolystyrene 10°C/minPolystyrene 5°C/minPolystyrene 1°C/min
Universal V4.2D TA Instruments
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Mass Effect – Semi-crystalline PE
436.28°C 457.57°C
-20
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40
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120
We
igh
t (%
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Temperature (°C)
0.492mg48.422mg
Universal V3.8A TA Instruments
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Shift in Onset with Ramp Rate
524.26°C 563.82°C
-20
0
20
40
60
80
100
120
We
igh
t (%
)
400 450 500 550 600 650 700
Temperature (°C)
2.5°C/min5°C/min10°C/min20°C/min
Universal V3.7A TA Instruments
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Typical Applications
•Thermal Stability
•Compositional Analysis
•Oxidative Stability
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Thermal Stability of Polymers
Method Log: 1:Select gas: 1 - N21: Ramp 20.00 °C/min to 650.00 °C2: Select gas: 2 - Air3: Ramp 20.00 °C/min to 1000.00 °C
PVC
PMMA
PET
650.00°C55.59%
650.00°C5.928%
LDPEPEEK
650.00°C14.32%
0
20
40
60
80
100
We
igh
t (%
)
50 250 450 650 850 1050
Temperature (°C)
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TGA of an Adhesive
0
1
2
3
De
riv.
We
igh
t (%
/°C
)
0
20
40
60
80
100
We
igh
t (%
)
0 100 200 300 400 500 600
Temperature (°C)
25.18mg of an adhesive @ 10°C/min
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Inset View Shows Strange Result
0
1
2
3
Deri
v. W
eig
ht
(%/°
C)
0
20
40
60
80
100
Weig
ht
(%)
0 100 200 300 400 500 600
Temperature (°C)
Is this real?
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Use time based derivative of
temperature to plot the heating
rate
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Aberration in Heating Rate
5
10
15
De
riv.
Te
mp
era
ture
(°C
/min
)
-1
0
1
2
3
De
riv.
We
igh
t (%
/°C
)
0
20
40
60
80
100
120
We
igh
t (%
)
430 440 450 460 470 480
Temperature (°C)
Usually means that the sample touched the
thermocouple
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Typical Applications
•Thermal Stability
•Compositional Analysis
•Oxidative Stability
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PET w/ Carbon Black Filler
78.64%(11.26mg)
20.64%(2.957mg)
Carbon Black Filled PET
In N220.00 °C/min to 650.00 °CSwitch to AirRamp 20.00 °C/min to 1000.00 °C
-0.5
0.0
0.5
1.0
1.5
2.0
Der
iv. W
eigh
t (%
/°C
)
0
20
40
60
80
100
Wei
ght (
%)
0 200 400 600 800 1000
Temperature (°C)
How much Carbon Black was in this sample?
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PET
85.65%(16.01mg)
13.99%(2.614mg)
In N220.00 °C/min to 650.00 °CSwitch to AirRamp 20.00 °C/min to 1000.00 °C
PET
-0.5
0.0
0.5
1.0
1.5
2.0
De
riv.
We
igh
t (%
/°C
)
0
20
40
60
80
100
We
igh
t (%
)
0 200 400 600 800 1000
Temperature (°C)
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Comparison of Filled & Un-Filled PET
85.65%(16.01mg)
13.99%(2.614mg)
78.64%(11.26mg)
20.64%(2.957mg)
Method Log:1: Ramp 20.00 °C/min to 650.00 °C2: Select gas: 23: Ramp 20.00 °C/min to 1000.00 °C
6.65% Carbon Black
0
20
40
60
80
100
We
igh
t (%
)
0 200 400 600 800 1000
Temperature (°C)
PETFilled PET
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Filled Polymer Analysis
Polymer
Carbon Black
Air(A)
Polymer
Carbon Black
Air(B)
"Light" Oil
Polymer +"Heavy" Oil
Carbon Black
Air(C)
\\\\\\ \\
100
0100
1000
0
WE
IGH
T (
%)
TEMPERATURE (°C)
Inert filler
Inert filler
Inert filler
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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.
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Kinetic Analysis, con’t.
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.
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TGA Kinetics
• 1st Order Kinetics based on Flynn and Wall method
• Lifetime Estimation based on Toops and Toops method
• PTFE tested at 1, 5, 10 and 20 deg/min
• Sample sizes constant
• Nitrogen purge
• Conversion levels selected at 1, 2.5, 5, 10 and 20%
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Common Thermogram with TGA Scans
75
80
85
90
95
100
105
Wei
ght (
%)
400 450 500 550 600 Temperature (°C) T A Instruments
1.0%
2.5%
5.0%
10.0%
20.0%
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Log Heating Rate versus 1/T
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Log[
Hea
ting
Rat
e (°
C/m
in)]
1.15 1.20 1.25 1.30 1.35 T A Instruments
1.0%
2.5%
5.0%
10.0%
20.0%
Check for linearity
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Activation Energy by MTGA
282.51°C 95.00%
282.50°C167.2kJ/mol
Ethylene Vinyl Acetate - 17.86mgMTGA - 5/200@1°C/min
100
200
300
400
500
600
700
800
900
Activa
tion
En
erg
y (
kJ/m
ol)
-0.2
0.0
0.2
0.4
0.6
0.8
Deri
v. W
eig
ht (%
/°C
)
70
80
90
100
Weig
ht
(%)
100 150 200 250 300 350 400
Temperature (°C) Universal V4.3A TA Instruments
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Sample of TGA Application Briefs
• H-16781 “Thermogravimetry-Mass Spectrometry Using a Simple Capillary Interface”
• TA023 “Thermal Analysis Review: High Resolution TGA - Theory and Applications”
• TA075 “High Resolution TGA Kinetics”
• TA 122 “Determination of Carbon Black Pigment in Nylon 66 by TGA”
• TA 125 “Estimation of Polymer Lifetime by TGA Decomposition Kinetics”
• TA231 “TGA Evaluation of Zeolite Catalysts”
• TN6 “Consideration of Subtle Experimental Effects (Simultaneous TGA-DTA)”
• TN24 “TGA Temperature Calibration Using Curie Point Standards”
• TN40 “Optimizing Stepwise Isothermal Experiments in Hi-Res TGA”
• TS13 “Clarification of Inorganic Decomposition by TG-MS”
• TS39 “Characterization of Polyurethane by TGA and Hi-Res TGA”
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Common TGA Parts & Accessories
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Common TGA Parts & Accessories
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Need Help?
•Check the online manuals and error help.
•Contact the TA Instruments Hotline
Phone: 302-427-4070 M-F 8-4:30 EST
Select Thermal or Rheology Support
Email: [email protected] or
•Call the TA Instruments Service Hotline
Phone: 302-427-4050 M-F 8-4:30 EST
•Call your local Technical or Service Representative
•Check out our Website: www.tainstruments.com