Thermogravimetric Analysis(TGA)

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.

TGA: What TGA Can Tell You

Composition of Multicomponent SystemsThermal Stability of MaterialsOxidative Stability of MaterialsEstimated Lifetime of a ProductDecomposition Kinetics of MaterialsThe Effect of Reactive or Corrosive Atmosphereson MaterialsMoisture and Volatiles Content of Materials

TGA: Environment Considerations

Avoid areas near heater or air conditioner ducts

Avoid tables with drawers or those near a door

For optimum results, use a marble table

TGA: Purge Gas Guidelines

TGA: Always purge through balance housing withdry inert gas (i.e. Nitrogen)

TGA: Only introduce reactive/corrosive gasesthrough sample area/furnace housing

TGA 2950 Standard Furnace

100mL/min. total:40mL/min. balance60mL/min. furnace

TGA 2050/2950 EGAFurnace

100mL/min. total:10mL/min. balance90mL/min. furnace

TGA: Purge Gas Flow Rates

TGA: Purge Gas

Nitrogen most common

Helium often provides best baseline

Air can sometimes improve resolution because ofdifferences in the oxidative stability (versus thermal stability) of components

TGA: Cool-down Between Scans

TGA 2050, 2950Select air cool as method end condition2050: Furnace cools to 500°C, then air cools2950: Furnace opens, then air cools

TGA: 2050, 2950 - Mass Calibration

Two point mass adjustment100mg. range (use 100mg. weight)1000mg. range (use 1000mg. weight)

Run TGA weight calibration routine

Follow screen instructions to tare and masscalibrate using two calibration weights (if known,enter exact mass of calibration weights)

TGA: Temperature Calibration

Curie Point Transition MethodTGA 2050, 2950

ASTM 1582 - Standard Practice for Calibration of Temperature Scale for Thermogravimetry

Paramagnetic - a material that is susceptible toattraction by a magnet

Curie Point Temperature - that temperature wherethe material loses its magnetic susceptibility(defined as offset point)

Requires a magnet and well characterized transition materials

TGA: Temperature Calibration -Curie Point Transition Method

TGA: Temperature Calibration -Curie Point Transition Method

Magnet

Vertical Balance Configuration - TGA 2050/2950

Sample

Tare

Furnace

Attraction of Sample to MagnetResults in Initial Weight Gain

%

temp

Offset

TGA: Temperature Calibrationwith Magnetic Standards

200 250 300 350 400Temperature (°C)

95

100

105

110

115

120

125W

eig

ht

(%)

NICKEL THEORETICAL 354°C

361.15°C

TGA: Certified Calibration Kit

Certified Temperature Calibration Kit(P/N 952384-901)

Secondary Temperature Calibration Materials (Nickel, Alumel)Curie Temperatures traceable to National Reference Laboratories (NIST, LGC)Universal MagnetASTM E1582 test methodDetailed ISO style calibration instructions

TGA: Baseline Considerations

Especially important for measuring small weightlosses associated with volatilization or smallamounts of residue

Run clean empty tared pan, over temperaturerange of interest @ desired heating rate.

Plot weight in µg vs. temperature.

TGA: Measuring TGA Baseline Performance

-25

-20

-15

-10

-5

0

We

igh

t (µ

g)

0 200 400 600 800 1000

Temperature (°C)

Sample: BaselineSize: 0.0020 mgMethod: Ramp 20 w/ Init Iso

TGAFile: G:...\Transfer\LEWbsln1.001Operator: Louis WaguespackRun Date: 7-Dec-1999 14:48

TGA: Reproducibility of TGA Baseline

600.00°C-25.04µg

600.00°C-20.10µg

-30

-20

-10

0

10

We

igh

t (µ

g)

0 200 400 600 800 1000

Temperature (°C)

Six TGA Baselines @ 20°C/min2950 TGA w/ Std Furnace and N2 Purge

TGA:Effect of Heating Rate on Baseline

20°C/min

50°C/min

-25

-20

-15

-10

-5

0

5

We

igh

t (µ

g)

0 200 400 600 800 1000

Temperature (°C)

Effect of Heating Rate on 2950 baseline20° & 50°C/min w/ Std furnace and Nitrogen purge

TGA: Factors Influencing Baseline

Stability of table

Hang down wire condition

Hang down tube condition

Leveling of TGA

Cleanliness of Furnace

Purge gas flow rates

TGA: Sample Preparation

Maximize the surface area of the sample toimprove weight loss resolution and temperaturereproducibility

–Sample weight10-20mg for most applications50-100mg for measuring volatiles

Most TGA instruments have baseline drift of +/-0.025mg which is 0.25% of a 10mg sample

TGA: Typical Applications

Thermal Stability

Compositional Analysis

Oxidative Stability

TGA: Evaluation of High Temperature Polymers

0 100 200 300 400 500 600 700 800

0

20

40

60

80

100

TEMPERATURE (°C)

WE

IGH

T P

ER

CE

NT PVC

PMMA HPPE PTFEPI

wt. : 10 mgprog.: 5°Catm.,: N

2

TGA: Block versus Random Copolymers

0 100 200 300 400 5000

50

100

Temperature (°C)

Wei

gh

t (%

)

S - α MS

RANDOM

S - α MS BLOCK

P - α MS

PS

size: 8 mgprog: 6°C/minatm: 300 Pa vacuum

TGA: Calcium Oxalate

0 200 400 600 800 100020

40

60

80

100

120

-2

0

2

4

6

8

10

Temperature (°C)

Wei

gh

t (%

)

[---

----

----

-]D

eriv

. Wei

gh

t (%

/min

)

12.3%WATER 19.2% CO

30.0% CO2

TGA: EVA COPOLYMERS[J. Chiu, Appl. Polym. Sym., 2, 25 (1966)]

200 300 400 500 600 700

0

50

100

TEMPERATURE (°C)

WE

IGH

T P

ER

CE

NT

23%

390°

VA(%) = 23% x86.160.1

= 33

size : 100 mgprog : 5°C/minatm : N 2

Acetic Acid

Vinyl acetate (VA) %= wt loss of acetic acid x mol wt of VA / mol weight of acetic acid

TGA: EPDM Rubber Analysis

0 200 400 600 800 1000

0

20

40

60

80

100

-0.5

0.0

0.5

1.0

1.5

2.0

Temperature (°C)

Wei

gh

t (%

)

Der

iv. W

eig

ht

(%)

Switch to Air

24.96% Carbon Black + Ash

(5.656mg)

TGA: Vegetable Oil Oxidative Stability

0 10 20 30 40 50 60 70 80 90

25

50

75

100

125

TIME (Min.)

TE

MP

(°C

)

137-

WE

IGH

T C

HA

NG

E

+

Sample Size: 5.18 mgTemperature: 137°CAtmosphere: 0 at 50 mL/min

2

0 2

0.05

57 MINUTESFIRST DEVIATION

TGA: Standard TGA

Means of Enhancing ResolutionSlower Heating RateReduced Sample SizeChange Purge GasPin-hole Hermetic Pans

TGA: Conventional TGA - CalciumSulfate Dihydrate (Open Pan)

105

100

95

90

85

80

75

0.6

0.4

0.2

0.0

-0.20 50 100 150 200 250 300 350

Temperature (°C)

Wei

ght (

%)

[

]Der

iv.

Wei

ght

(% /

°C

)

TGA: Conventional TGA - CalciumSulfate Dihydrate (Pinhole Lid)

105

100

95

90

85

80

750 50 100 150 200 250 300

Temperature (°C)

Wei

ght (

%)

350

0.8

0.6

0.4

0.2

0.0

-0.2 [

]D

eriv

. Wei

ght (

% /

°C)

TGA: Hi-Res TGA - Alternate Methods

Dynamic (Hi-Res) TGAConstant Reaction Rate TGAStep Wise Isothermal TGA

TGA: Hi-Res TGA - What is Automated Stepwise Isothermal TGA?

Heating stops (isothermal) once a certain operator defined weight loss rate is exceeded then restarts after this rate falls below a second operator defined value.

TGA: Hi-Res TGA - Automated Stepwise Isothermal

AdvantagesSample held isothermal until transition completed - thus excellent resolution of overlapping transitions Permits careful control of reaction environmentAvailable on all TA Instruments TGA's

DisadvantagesDifficult method development. May require several scans to optimize run conditionsInappropriate parameter choices may produce artifactsLong run time

UtilityRoutine Analysis of similar samples

TGA: Hi-Res TGA (SWI) - Effect of EntranceThreshold on Transition Onset

300 350 400 450 500 55070

80

90

100

110

68

78

88

98

108

Temperature (°C)

[

] T

GA

Wei

gh

t (%

)

[

] T

GA

Wei

gh

t (%

)

1%/min

3%/min

4%/min5%/min

TGA: Hi-Res TGA (SWI)Typical SWI Thermal Method

1. Abort next segment if %/min > 5.02. Ramp 10°C/min to 1000°C3. Abort next segment if %/min < 0.54. Isothermal 1000 min5. Repeat 1 until 1000°C

TGA: Hi-Res TGA (SWI) - Effect ofThreshold Ratio on Transition End

350 400 450 500 550-10

0

10

20

30

40

50

Temperature (°C)

TG

A W

eig

ht

(%)

1/1.7

1/2

1/5

1/10

1/ 20

1%/min. Exit Threshold, x%/min. Entrance Threshold

* Note: Curves have been shifted relative to the y-axis to facilitate comparison

Exit.THEnt. TH

TGA: Conventional TGAPoly(vinyl acetate)

0 100 200 300 400 500 600 700-20

0

20

40

60

80

100

120

-10

0

10

20

30

40

Temperature (°C)

Wei

gh

t (%

)

[

]D

eriv

. Wei

gh

t (%

/min

)

Conventional TGA: ß = 20°C/min.

TGA: Conventional TGAPoly(vinyl acetate) - Scouting run

0 100 200 300 400 500 600 700-20

120

-10

0

10

20

30

40

Temperature (°C)

[

]D

eriv

. Wei

gh

t (%

/min

)

Conventional TGA: ß = 20°C/min.

Entrance Threshold:1/10 (P)

Exit Threshold:<1/10 (Ent. TH)

Entrance Threshold:1/10 (P)

Exit Threshold:<1/10 (Ent. TH)

P

TGA: Hi-Res TGASWI - Poly(vinyl acetate)

0 100 200 300 400 500 600 700-20

0

20

40

60

80

100

120

-2

0

2

4

6

8

10

12

Temperature (°C)

Wei

gh

t (%

)

Der

iv. W

eig

ht

(%/m

in)

TGA: Poly(vinyl acetate)Comparison of Modes

110

-10

10

30

50

70

90

200 300 400 500 600Temperature (°C)

Wei

gh

t (%

)

--- Conventional.... Dynamic__ Stepwise Isothermal

TGA: Comparison of Modes (cont.)

ModeMethod development

(min)Run time

(min)

Linear <1 34

Dynamic <1 50

SWI >40 180

TGA: TGA Kinetics -Wire Insulation Thermal Stability

200 250 300 350 400 450 500

80

85

90

95

100

Temperature (°C)

WE

IGH

T L

OS

S (

%)

0.5%1.0%2.5%

5%

10%

20%

10°C5°C

2.0°C1.0°C

size: 60mgatm.: N 2

Conversion

Wire Insulation ThermalStability

TGA: TGA Kinetics -Heating Rate verses Temperature

1.4 1.5 1.6

1

2

5

10

1000/T (K)

HE

AT

RA

TE

(°C

/min

)460 440 420 400 380 360

2010 5 2.5 1.0 0.5

Conversion

TGA: TGA Kinetics -Estimated Lifetime

TEMPERATURE (°C)

1.51.61.71.81.910

100

1000

10000

100000

1000000

1000/T (K)

ES

TIM

AT

ED

LIF

E (

hr.

)

260 280 300 320 340 3601 century

1 decade

1 yr.

1 mo.

1 week

1 day

ES

TIM

AT

ED

LIF

E

ThermoStar + TGA 2950

Mass Spectrometer Basics

• Overview of Mass Spectrometry

• Vacuum Requirements

• Ion Creation

• Ion Filtering

• Ion detection

Mass Spectroscopy

• A gas phase compound is ionized, accelerated, then filtered according to it’s mass to charge ratio and detected

• The ionization process typically breaks the compound into fragments, each with it’s own mass to charge (m/e) ratio

• The largest m/e detected is called the parent ion and corresponds to the molecular weight of the compound.

• The pattern of fragments detected is the mass spectrum of the compound and can be used for qualitative identification

Vacuum Requirements

• Filament Longevity

• Ion Mobility

• Detector Operation

Typical Vacuum ~ 10E-05 Torr

HH

e -

Gas Density ~ 1013 Molecules /m3

(@ 760 T ~ 1025 Molecules /m3 )

+

The Atomic Model

12 C = 12 A.M.U.

= Electron ~ 0 AMU

= Neutron ~ 1 AMU

= Proton ~ 1AMU

1 AMU = 1.66 X 10 -27 Kg.

Isotope Patterns

Isotope Patterns

Isotope Patterns

Ionization

12 C + 1e- 12 C+ + 2e-

Atom Ion

Ionization

m/e=6

1 e- + 12C12C++ + 3e-

1 e- + 18H2O

m/e=17

1 e- + 17OH 1 e- + 17OH 17OH+ +2 e-

Double Ionization

Fragmentation - Ionization

MassNumber Key Probable Additional Mass (m/e) fragments Parent Molecule(s) Number (m/e)

6 C++ CO 12, 28, 29C++ CO2 12, 28, 44C++ CxHy 12, 13, 14, 26, 27 etc.

12 C+ CO 28, 29C+ CO2 28, 29, 44C+ CxHy 13, 14, 26, 27 etc.

14 N+ N2 28, 29N+ NH3 15, 16, 17CH2+ CxHy 12, 13, 26, 27 etc.CO++ CO 28, 29

16 O+ O2 32, 34O+ H2O 17, 18CH4+ CH4 12, 13, 14, 15NH2+ NH3 14, 15, 17

17 OH+ H2O 16, 18NH3+ NH3 14, 15, 16

18 H2O+ H2O 16, 17

Some Key Fragment Ions

Typical Ion Formation

Spectrum of CO2 showing the 11 mostintense ions Natural

Abundance's

18O = 0.2%

13C = 1.1%

Filaments

Ions Out

Closed Ion Source

Neutral Gas Atom/Molecule

Electron

Ion

Gas In

Pressure(mBar)

Filaments

10-05 10-03 1010-04

Mass Filter

• Cylindrical Rods.• Stainless Steel or

Molybdenum.•Opposite Rods are

Connected Electrically.•Alignment is Critical

not adjustable.+

+

-

-

Mass Filter

Selected m/e ion - reaches detectorHigher m/e ion - deflected in z-axisLower m/e ion - deflected in y-axis

++ +++

++

I i

e-++

++

+

y

x

z

SEM

ION

SO

UR

CE

QUADRUPOLE ROD

QUADRUPOLE ROD

QUADRUPOLE ROD

Ion Detectors - Faraday

I ie-

I i ~ 10-14....10-9 A = Selected ion - positive charge

Indestructible Detector but gain = unity.

Cannot detect small ion currents <10-14 Amps.(Limit depends on electrometer only)

SEM Detector - Chaneltron

I i

GAIN ~ 100 106

set by SEM VOLTS

e-

e-

I i ~ 10-14....10-5 A

= Selected ion - positive charge-attracted into SEM by -ve dc volts.

SEMVOLTS ~ - 1500V dc

Can be destroyed by high currents>10-5 Amps , or by operation at highpressure.

MASS FILTER

ThermoStarPressure Conditions in the Gas Inlet

5 x 10-6 10-4 5 5 - 1000 mbar (approx.)

Transport vacuum

Gas In

TGA-MS: Capillary Interface

CONNECTOR TGA FURNACE

SAMPLE PAN

SILICA-LINED

STAINLESS STEEL

CAPILLARY

HEATING

CONNECTION

1 mm GAP

MOLECULAR LEAK

(SILICON CARBIDE FRIT)

TO MASS SPECTROMETER

QUADRUPOLE

TEFLON SEAL

TO SECOND STAGE

OF ROTARY PUMP

EGA Furnace

Swagelock Fitting

Silica CapillaryStainless Steel Sheath

Vespel Drilled Plug

Aluminum Bracket

Mass-Spec to EGA Furnace

Mass-Spec Benefits

• Additional information for the interpretation of the reactions in the TGA results

• Sensitive method for the analysis of gaseous reaction products

• Exact control of the furnace atmosphere before starting and during the experiment

• Location of air leaks around the furnace

TGA of Calcium Oxalate

-2

0

2

4

6

8

10

De

riv.

Weig

ht

(%/m

in)

20

40

60

80

100

120

We

igh

t (%

)

0 200 400 600 800 1000

Temperature (°C)

Sample: Calcium Oxalate MonohydrateSize: 17.6070 mgMethod: RT-->1000°C @ 20°C/min

TGA

Universal V2.7B TA Instruments

TGA-MS Calcium Oxalate

TGAderivative weight loss

H2Om/e=18

COm/e=28

CO2 m/e=44

0 200 400 600 800

Temperature (°C)

TGA-MS

-1

0

1

2

3

4

Der

iv. W

eigh

t (%

/min

)

90

92

94

96

98

Wei

ght (

%)

250 252 254 256 258 260 262 264 266

Time (min)

Sample: 583-35-ESize: 19.6330 mg TGA

Universal V2.7B TA Instruments

TGA-MS

TGA: Determination of PolymerComposition (EVA Copolymers)

0 100 200 300 400 500 600

0

20

40

60

80

100

120

Temperature (°C)

TG

A W

eig

ht

(%)

14% VinylAcetate

40% VinylAcetate

Initial Weight Loss(Acetic Acid) indicatesVinyl Acetate Level

0 100 200 300 400 500 600Temperature (°C)

MS

Inte

nsi

ty

14% VinylAcetate

40% VinylAcetate

Mass 60(AceticAcid)

Mass 56(Hydrocarbon)

TGA: Smoke Generation in FlameRetarded Polymers (PVC)

0 100 200 300 400 50020

40

60

80

100

Temperature (°C)

TG

A W

eigh

t (%)

MS

Inten

sity

PVC

PVC + MoO3

0 100 200 300 400 500Temperature (°C)

Benzene

(78 amu)