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)
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