TGA & SDT Theory and Applications Online Courses...Online Courses ©2020 TA Instruments Part 2: Applications Agenda 2 General Experimental Effects Thermal & Oxidative Stability Improving

08.05.2020

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TGA & SDT Theory and Applications

Online Courses

©2020 TA Instruments

Part 2: Applications

Agenda

2

General Experimental Effects

Thermal & Oxidative Stability

Improving Resolution

− Standard TGA

− Hi Resolution TGA (Hi-Res)

Decomposition Kinetics and Modulated TGA (MTGA)

Evolved Gas Analysis

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General Considerations

3

Experimental Effects

TGA Curves are not ‘Fingerprint’ Curves

4

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:

− Sample Mass

− Heating Rate

− Purge gas

− Sample volume/form and morphology

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Larger sample mass increases the observed decomposition temperature

5

0

20

40

60

80

100

We

igh

t (%

)

0 100 200 300 400 500 600

Temperature (°C)

Polystyrene 17.6 mgPolystyrene 10.2 mgPolystyrene 5.4 mgPolystyrene 2.7 mg

Universal V4.2D TA Instruments

Higher heating rates increase the observed decomposition temperature

6

0

20

40

60

80

100

Weig

ht (%

)

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

Sample Mass

10mg ±1mg

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High-Heating Rate TGA Analysis

7

60.09% Polypropylene(2.736mg)

0

20

40

60

80

100

Weig

ht (%

)

0 200 400 600 800 1000Temperature (°C) Universal V3.9A TA Instruments

500 °C/min

40°C/min

40% calcium

carbonate

High-Heating Rate TGA Analysis

8

7

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Sample Morphology Effects – PET

9

419.58°C 424.58°C

0

20

40

60

80

100

120

Weig

ht

(%)

0 100 200 300 400 500 600

Temperature (°C)

2.9 m g; am orphous PET2.8 m g; crystalline PET

Universal V3.8A TA Instrum ents

2.9 mg; amorphous PET

2.8 mg; semi-crystalline PET

Applications

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Thermal Stability of Polymers

1: Gas 1 (N2)

2: Ramp 20ºC/min to 650ºC

3: Gas 2 (air)

4: Ramp 20ºC/min to 1000ºC

Gas Switch

11

Block versus Random Copolymers

12

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Effect of Epoxy Cure Temperature

13

Residue determination using TGA

Sample: NaCl; 0.07% (wt/vol) in water

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EVA Copolymer

15

16.87% Acetic Acid(3.240mg)

-20

0

20

40

60

80

100

120

Weig

ht (%

)

0 100 200 300 400 500 600 700

Temperature (°C) Universal V3.3B TA Instruments

% Vinyl Acetate = % Acetic Acid *

Molecular Weight(VA) / Molecular

Weight (AA)

VA% = 16.85(86.1/60.1)

= 24.2%

Sample: EVA (25%)

Size: 19.2030mg

Heating Rate: 10°C/min

PET w/Carbon Black Filler

16

78.64%(11.26m g)

20.64%(2.957mg)

Carbon Black Filled PET

In N220.00 °C/m in to 650.00 °CSwitch to AirRam p 20.00 °C/m in to 1000.00 °C

-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)

How much

Carbon Black

was in this

sample?

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PET Without Filler

17

85.65%(16.01mg)

13.99%(2.614m g)

In N220.00 °C /m in to 650.00 °CSwitch to AirRam p 20.00 °C/m in to 1000.00 °C

PET

-0.5

0.0

0.5

1.0

1.5

2.0

Deri

v.

We

igh

t (%

/°C

)

0

20

40

60

80

100

Weig

ht (%

)

0 200 400 600 800 1000

Temperature (°C)

Comparison of Filled & Un-Filled PET

18

85 .65%(16 .01m g)

13 .99%(2 .614m g)

78 .64%(11 .26m g)

20 .64%(2 .957m g)

M e thod Log :1 : R am p 20 .00 °C /m in to 650.00 °C2 : S e lec t gas : 23 : R am p 20 .00 °C /m in to 1000 .00 °C

6.65% C arbon B lack

0

20

40

60

80

100

Weig

ht (%

)

0 2 00 40 0 60 0 800 10 00

Tem pera ture (°C )

PETFil led P ET

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Composite Analysis

19

EPDM Rubber Analysis

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Filled Polymer Analysis

21

Polymer

Carbon Black

Air(A)

Polymer

Carbon Black

Air(B)

"Light" Oil

Polymer +

"Heavy" Oil

Carbon Black

Air(C)

100

0

100

100

0

0

WE

IGH

T (

%)

TEMPERATURE (°C)

Inert filler

Inert filler

Inert filler

Effect of Flame-Retardant

22

0 200 400 600 800

60

70

80

90

100

TEMPERATURE (°C)

WE

IGH

T (%

)

Without Flame-Retardant

With Flame-

Retardant

Size: 20 mg

Prog.: 10°C/min

Atm.: Air

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TGA-MS of Flame-Retardant

0 100 200 300 400 500

20

40

60

80

100

Temperature (°C)

TG

A W

eig

ht (%

)

MS

Inte

nsity

PVC

PVC + MoO3

0 100 200 300 400 500

Temperature (°C)

Benzene

(78 amu)

Benzene is a component of smoke. Much reduced in the flame-retardant sample

Vegetable Oil Oxidative Stability

24

0 10 20 30 40 50 60 70 80 90

25

50

75

100

125

TIME (Min.)

TE

MP

(°C

)

137

-W

EIG

HT

CH

AN

GE

+ Sample Size: 5.18 mg

Temperature: 137°C

Atmosphere: 0 2

0 2

0.05

57 MINUTES

FIRST DEVIATION

Similar principle to OIT experiment done by DSC

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-2

1

4

7

Heat F

low

(W

/g)

-0.6

-0.3

0.0

0.3

0.6

0.9

Deriv. W

eig

ht (%

/°C

)

60

66

72

78

84

90

96

102

Weig

ht (%

)

0 200 400 600 800

Temperature (°C)

DSC-TGA Sodium Tungstate

Small Sample Size (3mg) and 10°C/min Heating Rate

Dehydration

Solid state and melting transitions

High Resolution TGA

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Temperature-controlled TGA (standard TGA) vs sample-controlled TGA

27

Temperature-controlled thermal analysis Sample-controlled thermal analysis

Ref:

O. Toft Sørensen and J. Rouquerol (2003). Sample Controlled Thermal Analysis: Origin, Goals, Multiple Forms, Applications and Future.

Kluwer Academic Publishers, Netherlands

Hi-Res TGA is a

sample-controlled

TGA method

Standard TGA: advantages

28

Easy to set up

When the individual decomposition steps occur at well-separated temperatures,

quantitative information for each step can be obtained

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Standard TGA: limitations

29

Complex thermal scans with broad weight losses

Overlapping weight losses

Multiple peaks/shoulders

Ref:

J-F. Masson, S. Bundalo-Perc, Thermochimica Acta, 436 (2005), 35–42

Standard TGA of bitumen

Weig

ht

(%

)

d(W

eig

ht) / d

(Tem

pera

ture

) d(W

eig

ht ) / d

() ((%

) / (°C))

Improving resolution in Standard TGA experiments

30

Means of Enhancing Resolution

Slower heating rate

Reduced sample size

Pin-hole hermetic pans (self-generating atmosphere)

Applicable to hydrates & solvates

Not applicable to all materials

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Impact of heating rate on resolution: 20°C/min

31

100

Temperature (°C)

150 200 250 300

110

100

90

80

70

60

0 50

WATER

10

8

6

4

2

0

-2

13 minutes

20°C/min

Weig

ht (%

)

(

) D

eriv.

Weig

ht (%

/min

)

Impact of heating rate on resolution: 1°C/min

32

0 50 100 150 200 250 300

60

70

80

90

100

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Temperature (°C)

170 MINUTES

1°C/min

(

) D

eriv.

Weig

ht (%

/min

)

Weig

ht (%

)

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Effect of sample mass on resolution: bitumen

33Ref:


Resolution enhancement using a pinhole hermetic DSC pans

34

Pt TGA pan

Tzero Hermetic Pinhole Lid

(75 µµµµm laser drilled pinhole)

Tzero pan

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Resolution enhancement using a pinhole hermetic DSC pans: gypsum

35

Heating gypsum between 100°C and 150°C (302°F) partially dehydrates the mineral by

driving off exactly one and a half moles of the water contained in its chemical structure

The partially dehydrated mineral is called calcium sulfate hemihydrate or calcined gypsum

(CaSO4·½H2O)

As heating continues, the anhydrite, CaSO4, is then formed.

CaSO4·½H2O + heat → CaSO4+ ½H2O

CaSO4·2H2O + heat → CaSO4·½H2O + 1½H2O (steam)

Theoretical Mass Losses of Gypsum

36

CaSO4·2H2O + heat → CaSO4·½H2O + 1½H2O

A loss of 1½H2O = 100*(MW. 1½H2O/ MW. CaSO4·2H2O)

= 15.69%

CaSO4·½H2O + heat → CaSO4+ ½H2O

A loss of ½H2O = 100*(MW. ½H2O/ MW. CaSO4·2H2O)

= 5.23%

Total weight loss = 15.69% + 5.23% = 20.92% (2 moles of H2O)

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Effect of DSC Pinhole pans on TGA resolution

37

14.90% (1.050mg)

4.830% (0.3405mg)

StandardTGA Pan

Pin HoleDSC Pan

0

1

2

[ –

– –

– ] D

eri

v. W

eig

ht

(%/°

C)

55

65

75

85

95

105W

eig

ht

(%)

0 50 100 150 200 250

Temperature (°C)

Gypsum

Theoretical: 15.69%

Theoretical: 5.23%

Sample-controlled TGA to improve TGA resolution

38

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Hi-Res™ TGA

In a Hi-Res™ TGA experiment the heating

rate is controlled by the rate of

decomposition

Faster heating rates during periods of no

weight loss, and slowing down the

heating rate during a weight loss –

therefore not sacrificing as much time

Hi-Res™ TGA can give better resolution or

faster run times, and sometimes both

39

Hi-Res™ TGA of Calcium oxalate

40

10000 100 200 300 400 500 600 700 800 900

Temperature (°C)

110

30

40

50

60

70

80

90

100

-0.25

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0.00

100

-100

-50

0

50

calcium oxalate - Hi-ResTM TGA

50°C/min, resolution 5, sensitivity 1

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Std TGA 20°C/minTime = 38.64 min

Std TGA 1°C/minTime = 771.46 min

Hi-Res TGA 50°C/min; Res 5Time = 125.29 min

0

20

40

60

80

100

We

ight

(%)

0 200 400 600 800

Temperature (°C) Universal V2.5D TA Instruments

Hi-Res™ TGA vs. Std TGA of Nylon/PE Blend

41

Programming a Hi-Res™ TGA experiment – Sensitivity Number

42

1.1.1.1. Sensitivity Sensitivity Sensitivity Sensitivity 1.01.01.01.0

2. Ramp 50°C/min, Res. 4.0 to 1000°C

SensitivitySensitivitySensitivitySensitivity: typically varies from 0 to 8.0

Controls the response of the Hi-Res system to changes in decomposition rates (D wt%/min)

Determines the increase in decomposition rate that warrants a reduction in the heating rate (or vice-

versa)

Higher sensitivity values increase sensitivity

Makes the Hi-Res system more responsive to small changes in the rate of reaction

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Programming a Hi-Res™ TGA experiment – Resolution Number

43

Sensitivity 1.0

Ramp 50°C/min, Res. Res. Res. Res. 4.04.04.04.0 to 1000°C

Resolution: typically varies from -8.0 to 8.0

Adjusts the heating rate based on the sample decomposition rate (wt%/min)

As the decomposition rate increases, the heating rate is further decreased (and vice-versa).

Higher resolution number (absolute value) results in higher resolution

Greater reduction in heating rate at smaller values of wt%/min

Also increases the time of the experiment

Two modes of Hi-ResTM TGA

44

Hi-ResTM TGA

Dynamic mode

(wt%/min is variable)

Constant reaction mode

(wt%/min is constant)

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Dynamic Mode

45

Positive resolution settings

Higher heating rate (e.g., 50˚C/min) for most materials

Start with 20°C/min for materials with low temperature (under 50-100 °C)

Heating rate never goes to zero

Preferred for fast survey scans of unknown samples over wide temperature ranges

Typically gives better resolution and/or faster time than standard TGA

Constant Reaction Mode

46

Negative resolution settings

Slower heating rate (1-10˚C/min); 5˚C/min is a good start

Furnace temperature is controlled to maintain a constant preselected rate of weight change

Preferred for any sample where it is important to limit or control the rate of reaction – may

include self-heating reaction, auto-catalyzing reactions, etc

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Optimizing the Hi-Res™ TGA settings

47

Good starting points

Sensitivity of 1111

Resolution of 4 4 4 4

Higher resolution number means slower heating rate, therefore, longer experiment time

Increase the resolution number if you need further separation of derivative peaks

Effect of sensitivity settings on TGA data

48

Res = 5 for all Hi-Res experiments

1 C/min std TGA

Sensitivity setting 1




50/50 KHCO3/NaHCO3 mixture

47

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Effect of resolution settings on TGA data

49

Overlay

Resolution = 1Sensitivity = 1

Resolution = 8Sensitivity = 1

Note that increasing resolution setting

increases the resolution of each

transition and simultaneously reduces

the transition temperature.

Resolution: 1

Resolution: 8

Sensitivity = 1 for all curves

Hi-Res TGA on ethylene-vinyl acetate copolymer

Compare Hi-Res™ TGA vs. standard TGA at 10°C/min –

50

Ethylene Vinyl Acetate copolymer

49

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Standard TGA 10°C/min of bitumen sample

51

Lower Temp

Region

Middle Temp

Region Higher Temp

Region

air purge

Ref:


Standard TGA vs Hi-Res™ TGA (dynamic mode) of bitumen sample

52

6000 100 200 300 400 500

Temperature (°C)

-1.00

1.25

1.00

0.75

0.50

0.25

0.00

-0.25

-0.50

-0.75

standard TGA

Hi-res TGA - dynamic mode

Ref:


Heating rate: 50 C/min

Res: 3

Sen: 5

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Constant Reaction Rate TGA of bitumen sample

53

350150 200 250 300

Temperature (°C)

0.0

1.0

0.5

Hi-res TGA - constant reaction rate

standard TGA

dm/dt = 0.316%/min

resolution: -4,

sensitivity: 1

Ref:


Hi-Res™ TGA- Advantages

54

Relatively simple to develop method

Rapid survey over wide temperature range with excellent resolution

High resolution with equal/better productivity, even on unknowns

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Automated Stepwise Isothermal TGA (SWI)

55

Heating stops (goes isothermal) when a certain rate of weight loss is reached, then resumes

after this rate falls below a second defined value

Operator defines the values for the rate of weight loss

Incorrect values can cause artifacts that appear as ‘additional’ mass losses

Correctly set up, can give excellent resolution, but takes quite a bit longer

Automated Stepwise Isothermal TGA (SWI)

56

Advantages

Sample held isothermal until transition completed - thus excellent resolution of overlapping

transitions

Permits careful control of reaction environment

Available on any TA Instruments TGA

Disadvantages

Requires method development. May require several scans to optimize run conditions

Inappropriate parameter choices may produce artifacts

Long run times

55

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Standard TGA of Polyvinyl Acetate

57

Basis for Entrance

Threshold

Ref:

Thermal Applications Note TN40 – Optimizing Stepwise Isothermal Experiments in Hi Res TGA

Typical SWI Thermal Method

58

1. Abort next segment if %/min > 4

2. Ramp 10°C/min to 1000°C

3. Abort next segment if %/min < 0.4

4. Isothermal 1000 min

5. Repeat 1 until 1000°C

57

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SWI of Polyvinyl Acetate

59Ref:

Thermal Applications Note TN40 – Optimizing Stepwise Isothermal Experiments in Hi Res TGA

Hi-Res™ TGA of lubricating oil

60

254.73°C

359.23°C

24.72% First Weight Loss Event(2.959m g)

39.05% Second W eight Loss Event(4.674mg)

-0.5

0.0

0.5

1.0

1.5

2.0

Deriv. W

eig

ht (%

/°C

)

20

40

60

80

100

120

We

ight (%

)

0 200 400 600 800 1000

Temperature (°C)

0 10 20 30 40 60 70 80 85

Time (min)

Universal V4.4A TA Instruments

Resolution factor = 4

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Hi-Res™ TGA of lubricating oil

61

205.52°C

325.71°C

412.42°C

22.66% First Weight Loss Event(2.854m g)

39.79% Second W eight Loss Event(5.012m g)

4.357% Third W eight Loss Event(0.5488m g)

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

De

riv.

Weig

ht

(%/°

C)

20

40

60

80

100

120

Weig

ht

(%)

0 100 200 300 400 500 600

Temperature (°C)

0 25 100 150 250 300 325 343

Time (min)

Universal V4.4A TA Instrum ents

Resolution factor = 6

Stepwise Isothermal TGA of lubricating oil

62

22.28% First Weight Loss Event(2.623mg)

35.93% Second Weight Loss Event(4.231mg)

5.655% Third Weight Loss Event(0.6660mg)

20

40

60

80

100

120

We

igh

t (%

)

0 100 200 300 400 500 600

Temperature (°C)

0 25 75 250 255

Time (min)

Universal V4.4A TA Instruments

61

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Decomposition Kinetics by MTGA™

63

Decomposition Kinetics Background

Includes isothermal and constant heating rate methods

Constant heating rate method is the fastest and will be discussed here

Ultimate benefit obtained in ‘Life-Time’ plots

Requires at least 3 TGA runs at different heating rates or 1 Modulated TGA® run

63

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Kinetic Analysis

65

The rate at which a kinetic process proceeds depends on the temperature the specimen is at,

and the time it has spent at that temperature

Typically kinetic analysis is concerned with obtaining parameters such as

Activation energy (Ea),

Reaction order (n), and

Generating predictive curves for conversion (�)

Fundamental equation for kinetics

66

dt

dα

T

f(T) f(α) dt

dα f(T)*f(α)dt

dα

dt

dα

T

f(T)dt

dα

T

f(T)dt

dα

T

f(T) f(α) dt

dα f(T)*f(α)dt

dαf(α) dt

dα f(T)*f(α)dt

dα

65

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Kinetics by TGA

67

��: � =�� − ��

�� − ��

0

T

Co

nve

rsio

n,

%

Initial weight:

win 100

Weight at T:

wT

Final weight:

wf

We

igh

t, %

��

Kinetic Analysis

68

Activation energy (Ea) can be defined as the minimum amount of energy

needed to initiate a chemical process.

State 1

State 2

Ea

67

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Decomposition Kinetics by TGA

69

Traditional methods include isothermal and constant heating rate techniques

ASTM E1641

Based on method of Flynn and Wall – Polymer Letters, 19, 323 (1966). Requires collection of

multiple curves at multiple heating rates

Weight (%)

Increasing

Heating Rate

Increasing

Heating Rate

Recipe for Activation Energy by ASTM E1641

70

Run TGA experiment on polymer at 4-6 different heating rates

Obtain a temperature at an isoconversional point – for example 10% weight loss for each

heating rate

Plot the ln of the heating rate (β) versus 1/T (temperature units must be in Kelvin)

Slope of the line is (-Ea/R). Multiply the slope of the line by –(8.314 x 10-3) to obtain the

activation energy in kJ/mol

TA Instruments Application Note TA251

Blaine, R. L. and Hahn, B. K., “Obtaining Kinetic Parameters by Modulated Thermogravimetry,” J. Therm.

Anal., Vol. 54, 1998, p. 694.

69

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PTFE Decomposition by ASTM E1641

71

10 % Conversion

PTFE Decomposition by ASTM E1641

72

Ea = 354.9 kJ/mol

71

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Advantages of MTGA™

73

One run needed to obtain activation energy

(ASTM E2958)

Activation energy is a signal in the data file

Comparable with Flynn-Wall method for calculated Ea with the benefit of the reduced time

Method works under quasi-isothermal or ramping conditions

Activation energy is obtained as a continuous curve and so can be manipulated numerous

ways. For example, it can be plotted as a function of conversion

Can be combined with Hi-Res™ to speed up experiments and more accurately handle

multiple weight loss events

Setting Up MTGA™ Experiment

74

• Three parameters must be defined:

• Heating rate

• Modulation period

• Modulation amplitude

• What is the effect of these parameters on the data? What are the optimum values?

73

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Setting Up MTGA™ Experiment - General Guidelines

75

Higher amplitudes improve signal/noise and increase precision but require longer periods to

make sure the sample is remaining in equilibrium

Longer periods ensure equilibrium but require slower ramp rates so the minimum 5 cycles

per transition can be obtained

A scouting run at 10 °C/min is useful to determine width of transitions

Range of consistent results:

Period = 200-300 s (practical range: 100 – 500s)

Amplitude = 3-5°C (practical range: 1 – 10°C)

Ramp Rate = 1 °C/min (practical range: 0.5 – 2 °C/min)

550450 475 500 525

Temperature (°C)

120

0

20

40

60

80

100

Weight (%)

MTGATM – Typical Values

Modulation period – 200 seconds

Amplitude – 5°C

Heating rate – 1°C/min

Plot derivative of weight loss and

calculate the width at half height of the

derivative weight loss peak.

− Need at least 5 modulation cycles

across this region.

76

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PTFE: Modulated Ramping Experiment

77

PolytetrafluoroethyleneNegligible weight

changeNegligible

weight

change

MTGA Precision: PTFE

78

Repeatability = 2.8X Standard Deviation

Conversion

(%) #1 #2 #3 #4 #5

Average

(kJ/mol)

Standard

Deviation

(kJ/mol)

Relative Stnd

Dev (%)

1 333.0 342.4 335.8 345.9 340 339.42 5.14 1.51

2 334.9 329.3 330.8 330.8 327.7 330.70 2.67 0.81

5 319.3 322.6 323.7 319.7 323.1 321.68 2.03 0.63

10 313.1 314 311.9 316.2 318.6 314.76 2.66 0.85

C.G. Slough The Accuracy, Repeatability, and Reproducibility of Activation Energy Values Measured by Modulated

Thermogravimetry. J of Testing and Evaluation V. 42, N. 6 (2014)

77

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PP: Modulated Ramping Experiment

79

Literature: Ea

= 232 ± 27 kJ/mol (12 % standard deviation)

This study: Ea

= 200 ± 19 kJ/mol (standard deviation 9.5 %)

TGA Kinetics - Estimated Lifetime

80

TEMPERATURE (°C)

1.51.61.71.81.910

100

1000

10000

100000

1000000

1000/T (K)

ES

TIM

AT

ED

LIF

E (

hr.

)

260 280 300 320 340 360

1 century

1 decade

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TA Instruments Application Note TA125

Estimation of Polymer Lifetime by TGA Decomposition Kinetics

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Evolved Gas Analysis

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Identification of Decomposition Products Using TGA/FTIR and TGA/Mass Spec

Why Use Evolved Gas Analysis?

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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

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TGA-EGA: Typical Applications

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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)

TGA-FTIR Advantages

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No solvents

No sample preparation

Rugged

Easy maintenance

Good sensitivity

Easy to use

Excellent for scouting or determining

presence of absence of species

Fast identification of functional groups

Search capabilities are really good –

Thermo Nicolet for example

Data interpretation can be challenging.

Generally, with EGA analysis, a strong

chemistry and analytical chemistry

background is needed

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EGA Example – TGA/FTIR

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The gases produced during thermal breakdown of the sample flow through a heated transfer

line into a gas cell where infrared radiation passes through.

The total infrared absorption and frequency as a function of time is stored in an array as the

Gram Schmidt file which is opened with the instrument software (Gram Schmidt

Reconstruction)

The Gram Schmidt reconstruction will typically resemble the derivative with respect to

temperature of the weight loss curve in the TGA experiment

Individual FTIR spectra are displayed by selecting points on the x-axis of the Gram Schmidt

reconstruction which has units of intensity as a function of time

Typically spectra can be searched using vendor supplied spectral data bases and fairly reliable

identifications of species can be made

Calcium Oxalate Monohydrate – TGA Data

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12.97%(1.695mg)

18.76%(2.451m g)

29.38%(3.840m g)

0.0

0.2

0.4

0.6

Deriv. W

eig

ht (%

/°C

)

20

40

60

80

100

120

We

ight (%

)

0 200 400 600 8 00 1000

Temperature (°C) Universal V4.4A TA Instrum ents

Water CO CO2

Mass = 13.07mg

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Calcium Oxalate – Water

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Calcium Oxalate – CO + CO2

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Calcium Oxalate – CO2

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TGA-FTIR: Analysis of Polyphenylene Oxide

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Gram-Schmidt

Reconstruction is

essentially a Total

IR Signal

Engineering polymer

-Heat resistant

-Good tensile properties

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473°C

Peak

intensity at

473 °C


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IR Spectrum @ Peak

intensity

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Reference Spectrum in Red

is 2,6 Dimethylphenol:

H

TGA-FTIR: Analysis of Nylon 6,6

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TGA-FTIR: Analysis of Nylon 66

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Water

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CO2

Ammonia

Water

Alkane

Amine

C=O

FTIR Library Search

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Libraries give the best single spectra match to the data presented

If multiple components are being emitted during a single weight loss event, the spectra will

be superimposed upon each other possibly leading to difficulties

The existence of searchable libraries does not relieve the analytical chemist from critically

analyzing the search results

ThermoNicolet FTIR software can attempt to deconvolute a spectrum to a maximum of four

components. Demonstration can be found in this TA Instrument webinar:

https://www.tainstruments.com/evolved-gas-analysis-tgaftir/

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TGA Mass-Spectrometry Benefits

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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

Discovery Mass Spectrometer – TGA / MS

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Advantages

No solvents

No sample preparation

Rugged

Easy maintenance

Good sensitivity

Easy to use

Excellent for scouting or determining presence of absence of species – great complement to GC / MS

Disadvantages

No search capability

Data interpretation can be

challenging (as with any unit mass

spectrometer)

Multiple software platforms for

data reduction

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TGA-MS: System Schematic

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The Discovery Mass Spectrometer (DMS)

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Benchtop, unit resolution quadrupole mass spec designed and optimized for evolved gas

analysis (EGA)

Quadrupole detection system includes:

Closed ion source

Quadrupole mass filter assembly

Dual detector system (Faraday and Secondary Electron Multiplier) ensuring excellent sensitivity

from ppb to percent concentrations

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TGA / MS

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Gases formed during the TGA experiment are drawn down a heated transfer line into the

mass spectrometer where they are ionized by an ion stream from the ion source, sorted by

the quadrupole mass filter and ultimately amplified and detected.

What is a Quadrupole Mass Spectrometer?

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Ionizes gas molecules and atoms

Electron impact knocks off an electron and fragments

molecules forming positive ions

Sorts by the mass/charge (m/z) ratio

Measures the ion current

Displays ion current vs. m/z ratio

When calibrated against inlet pressure - can display

partial pressure vs. m/z ratio

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TGA-MS Example: Aspirin

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MS Data Presentation

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Mass Spectrum of Aspirin


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What if I need help?

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TA Tech Tips

http://www.youtube.com/tatechtips

TA Instruments Applications Helpline available from the TA website

http://www.tainstruments.com/support/applications/applications-hotline/

Check out our Website

http://www.tainstruments.com/

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Thank You

The World Leader in Thermal Analysis, Rheology, and

Microcalorimetry

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TA Instruments –Waters LLC

www.tainstruments.com

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Documents

TGA & SDT Theory and Applications Online Courses...Online Courses ©2020 TA Instruments Part 2: Applications Agenda 2 General Experimental Effects Thermal & Oxidative Stability Improving