Thermal Gravimetric Analysis

Derrick Dean University of Alabama at Birmingham

Agenda

Definitions and review of instruments. Balance and furnace review. Mass and temperature calibration. Purge gas considerations. Sample preparation and pan selection. Method development. Miscellaneous.

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 1200C. 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

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).

TGA Furnaces Standard Furnace

Low mass Used for Hi-Res Runs Cools down in

TGA: Purge Gas Flow

60ml/min

90ml/min

10ml/min 40ml/min

Standard Furnace

EGA Furnace

SDT: Balance/Furnace Components

TGA/SDT: Purge Gas

Nitrogen most common.

Helium often provides best baseline but will make furnace work hard at high temperature.

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

Copper oxalate can be used to detect any oxygen contamination.

TGA: Sample Pans - Types/Sizes

Ceramic Platinum

Aluminum

50 L

100 L 100 L

250 L 500 L

Platinum and Aluminum pans have attached wire bail.

Ceramic pans have removable wire bail.

SDT: Sample Pans - Types/Sizes

Alumina: 40 L 90 L

Platinum: 40 L 110 L

TGA/SDT: Sample Pan Cleaning

All sample pans are reusable (except Aluminum)

Flame remaining residue from pan with torch (do not flame Aluminum pans)

Scrape off remaining ash (DSC fiberglass brush)

SDT cup bottom should be cleaned also to avoid sticking cup to beam.

Typical Methods

Ramp (heating) experiment: ex.: Ramp 20C/min. to 800C (Thermal Stability)

Ramp (heating) and Isothermal Hold

ex.: Ramp 20C/min. to 800C Iso 10 min.

Typical Methods (cont.)

Ramp and switch gas ex.: Ramp 20C/min. to 650C Select gas: 2 Ramp 20C/min. to 1000C (carbon black content)

High Resolution Ramp

ex.: Ramp 50C/min. res 5 to 800C (resolve closely spaced peaks)

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

0

20

40

60

80

100

Wei

ght (

%)

0 100 200 300 400 500 600Temperature (C)

Polystyrene 17.6 mgPolystyrene 10.2 mgPolystyrene 5.4 mgPolystyrene 2.7 mg

Universal V4.2D TA Instruments

Effect of Heating Rate

0

20

40

60

80

100

Wei

ght (

%)

0 100 200 300 400 500 600Temperature (C)

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

Universal V4.2D TA Instruments

Mass Effect Semi-crystalline PE

436.28C 457.57C

-20

0

20

40

60

80

100

120W

eigh

t (%

)

0 100 200 300 400 500 600Temperature (C)

0.492mg48.422mg

Universal V3.8A TA Instruments

Pan Shape Effect Amorphous PMMA

365.01C 369.13C

-20

0

20

40

60

80

100

120W

eigh

t (%

)

0 100 200 300 400 500Temperature (C)

4.6mg; spread evenly4.6mg; in tall S.S. pan (150 mg)

Universal V3.8A TA Instruments

Sample Morphology Effects PET

419.58C 424.58C

0

20

40

60

80

100

120

Wei

ght (

%)

0 100 200 300 400 500 600Temperature (C)

2.9 mg; amorphous PET2.8 mg; crystalline PET

Universal V3.8A TA Instruments

2.9 mg; amorphous PET

2.8 mg; semi-crystalline PET

Shift in Onset with Ramp Rate

524.26C 563.82C

-20

0

20

40

60

80

100

120W

eigh

t (%

)

400 450 500 550 600 650 700Temperature (C)

2.5C/min5C/min10C/min20C/min

Universal V3.7A TA Instruments

Typical Applications

Thermal Stability Compositional Analysis Oxidative Stability

Typical Applications

Thermal Stability Compositional Analysis Oxidative Stability

Calcium Oxalate Decomposition

1st Step CaC2O4H2O (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

0.0

0.6

[

] De

riv. W

eigh

t (%

/C)

20

40

60

80

100

Wei

ght (

%)

0 200 400 600 800Temperature (C)

Calcium Oxalate Repeatability Overlay of 8 runs, same conditions

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

650.00C55.59%

650.00C5.928%

LDPEPEEK

650.00C14.32%

0

20

40

60

80

100

Weig

ht (%

)

50 250 450 650 850 1050Temperature (C)

Block versus Random Copolymers

0 100 200 300 400 5000

50

100

Temperature (C)

Wei

ght (

%)

S - MS

RANDOMS - MS BLOCK

P - MS

PSsize: 8 mgprog: 6C/minatm: 300 Pa vacuum

Effect of Epoxy Cure Temperature

260 280 300 320 340 360 380 400 420 4400

20

40

60

80

100

Temperature (C)

Wei

ght (

%)

100C 125C

150C175C

200C

Prog: 10C/min

Alumel and Nickel Currie Standards

99.5

100.0

100.5

101.0

101.5

Wei

ght (

%)

0 100 200 300 400 500Temperature (C)

Alumel 157.00C

Nickel 368.80C

Initial weight gain with placement of magnet

Residue Determination - 0.2% Salt Solution

Residue:0.2212%(0.2160mg)

Method Log:1: Ramp 5.00 C/min to 90.00 C2: Isothermal for 120.00 min3: Ramp 5.00 C/min to 600.00 C4: End of method

0

20

40

60

80

100

Wei

ght (

%)

0 50 100 150 200 250Time (min)

Universal V3.2A TA

Sample: NaCl 0.2% in H2O Size: 97.6300mg

TGA of an Adhesive

0

1

2

3

Deriv

. Weig

ht (%

/C)

0

20

40

60

80

100

Weig

ht (%

)

0 100 200 300 400 500 600Temperature (C)

25.18mg of an adhesive @ 10C/min

Aberration in Heating Rate

5

10

15

Deriv

. Tem

pera

ture (

C/m

in)

-1

0

1

2

3

Deriv

. Weig

ht (%

/C)

0

20

40

60

80

100

120

Weig

ht (%

)

430 440 450 460 470 480Temperature (C)

Usually means that the sample touched the thermocouple

TGA of Drug A

Sample: Drug A Size: 22.5850mg Heating Rate: 10C/min

TGA of Drug A Monohydrate

4.946%(0.7505mg)

-2

0

2

4

6

Deriv

. Wei

ght (

%/m

in)

80

85

90

95

100

105

Wei

ght (

%)

0 50 100 150 200 250 300Temperature (C)

Universal V3.4C TA Instruments

Sample: Drug A Monohydrate Size: 15.1740mg Heating Rate: 10C/min

Water weight loss

Decomposition

TGA of Drug A Microspheres

Sample: Drug A Microspheres Size: 14.2940mg Heating Rate: 10C/min

TGA Analysis of Cold/Allergy Tablet

1.154%(0.2134mg)

2.346%(0.4338mg)

0

2

4

6

8

10

12

14

Deriv

. Wei

ght (

%/m

in)

50

60

70

80

90

100

Wei

ght (

%)

0 50 100 150 200 250 300Temperature (C)

Universal V3.4C TA Instruments

Sample: