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

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

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.

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

Calcium Oxalate Example

12.57% Water(0.8753mg)

19.47% Carbon Monoxide(1.355mg)

30.07% Carbon Dioxide(2.093mg)

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Temperature (°C)

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

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).

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.

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

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

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

TGA: Purge Gas Flow

60ml/min

90ml/min

10ml/min40ml/min

Standard Furnace

EGA Furnace

Standard Furnace

EGA Furnace Schematic

Quartz Liner

Off-Gases

Balance Purge

Sample Thermocouple

SamplePan

Furnace Core

Purge Gas InLow internal

Volume ~15ml

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.

TGA: Q Series MFC and GSA

MFC and GSA standard on Q500 and optional on Q50

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.

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.

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

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

Quantifying TGA Baseline Performance

Temperature or Time

Un

nor

mai

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Sam

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Mas

s

Drift

19.24µg

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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

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.

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)

Mass Loss And Residue Validation

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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

• 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

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

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.

Standards Can Be Run Simultaneously

99.5

100.0

100.5

101.0

101.5

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t (%

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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

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

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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Calcium Oxalate Repeatability

Overlay of 8 runs, same conditions

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%

General Considerations(Experimental Effects)

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:

Effect of Sample Size on Decomposition Temperature

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Polystyrene 17.6 mgPolystyrene 10.2 mgPolystyrene 5.4 mgPolystyrene 2.7 mg

Universal V4.2D TA Instruments

Effect of Heating Rate on Decomposition Temperature

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Polystyrene 20°C/minPolystyrene 10°C/minPolystyrene 5°C/minPolystyrene 1°C/min

Universal V4.2D TA Instruments

Mass Effect – Semi-crystalline PE

436.28°C 457.57°C

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0.492mg48.422mg

Universal V3.8A TA Instruments

Shift in Onset with Ramp Rate

524.26°C 563.82°C

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Temperature (°C)

2.5°C/min5°C/min10°C/min20°C/min

Universal V3.7A TA Instruments

Typical Applications

•Thermal Stability

•Compositional Analysis

•Oxidative Stability

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%

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TGA of an Adhesive

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25.18mg of an adhesive @ 10°C/min

Inset View Shows Strange Result

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Is this real?

Use time based derivative of

temperature to plot the heating

rate

Aberration in Heating Rate

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Usually means that the sample touched the

thermocouple

Typical Applications

•Thermal Stability

•Compositional Analysis

•Oxidative Stability

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

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How much Carbon Black was in this sample?

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

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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

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PETFilled PET

Filled Polymer Analysis

Polymer

Carbon Black

Air(A)

Polymer

Carbon Black

Air(B)

"Light" Oil

Polymer +"Heavy" Oil

Carbon Black

Air(C)

\\\\\\ \\

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TEMPERATURE (°C)

Inert filler

Inert filler

Inert filler

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.

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.

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%

Common Thermogram with TGA Scans

75

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105

Wei

ght (

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400 450 500 550 600 Temperature (°C) T A Instruments

1.0%

2.5%

5.0%

10.0%

20.0%

Log Heating Rate versus 1/T

0.2

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1.0

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Log[

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e (°

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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

Activation Energy by MTGA

282.51°C 95.00%

282.50°C167.2kJ/mol

Ethylene Vinyl Acetate - 17.86mgMTGA - 5/200@1°C/min

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Activa

tion

En

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ol)

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Temperature (°C) Universal V4.3A TA Instruments

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”

Common TGA Parts & Accessories

Common TGA Parts & Accessories

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: thermalsupport@tainstruments.com or

rheologysupport@tainstruments.com

•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