Thermal Gravimetric Analysis (TGA).pdf

TGA

1. Thermal Gravimetric Analysis (TGA)

2. Contents:
1
•Introduction
•Types
•Principle
•ThermogravimetricanalysisCurve
•Instrumentation
•Factorsaffectingresults
•Advantages
•Limitations
•Applications

3. Thermogravimetricanalysis
Definition
•A formof vitalizationgravimetryinwhich thechangeina
samplesmas ismonitoredwhileitisheated.
•Inthermogravimetry,thesamplesmassiscontinuously
monitoredwhile theappliedtemperatureisslowlyincreased.
•Theproductofsuchthermaldecompositionisindicatedbya
stepinthethermogram,thechangeinmassateachstepcanbe
usedtoidentifyboththevolatizedspeciesand thesolid
residue.

4. 4
Typesofthermogravimetry:
1.Isothermalorstaticthermogravimetry:Inthistechnique
thesampleweightisrecordedasfunctionoftimeatconstant
temperature.
2.Quasistaticthermogravimetry:In thistechniquethesample
isheatedtoconstantweightateachofseriesofincreasing
temperatures.
3.Dynamicthermogravimetry:Inthistechniquethesampleis
heatedinanenvironmentwhosetemperatureischangingina
predeterminedmannergenerallyatlinearrate.Thistypeis
generallyused.

5. 5
PrincipleofTGA:
•Inthermo-gravimetricanalysis,thesampleisheatedinagiven
environment(air,N2,CO2,He,Ar,etc.)atcontrolledrate.The
changeintheweightofthesubstanceisrecordedasafunction
oftemperatureortime.
•Thetemperatureis increasedat aconstantrate foraknown
initialweightofthesubstanceandthechangesinweightsare
recordedasafunctionoftemperatureatdifferenttimeinterval.
•Thisplotofweightchangeagainsttemperatureiscalled
thermo-gravimetriccurveorthermo-gram,thisisthebasic
principleofTGA.

6. TGAcurve:
•Theinstrumentusedfor
themo-gravimetryisa
programmedprecision
balanceforriseintemperature
knownasThermo-balance.
•Resultsaredisplayedby aplot
ofmasschangeversus
temperatureortimeandare
knownasThermogravimetric
curvesorTGcurves.
6

7. 7
TGAcurve:
•TGcurvesarenormallyplottedwiththemasschange(Dm)in
percentageonthey-axisandtemperature(T)ortime(t)onthe
x-axis.
•Therearetwotemperaturesinthereaction,Ti(procedural
decompositiontemp.)andTf(finaltemp.)representingthe
lowesttemperatureatwhichtheonsetofamasschangeisseen
andthelowesttemperatureatwhichtheprocesshasbeen
completedrespectively.
•Thereactiontemperatureandinterval(Tf-Ti)dependonthe
experimentalcondition;therefore,theydonothaveanyfixed
value.

8. TGAcurveofAgNO
3:
8

9. InstrumentationofTGA:
9

10. InstrumentationofTGA:
•Recordingbalance
•Sampleholder
•Furnace
•Temperatureprogrammer/controller(thermocouple)
•Recorder
10

11. 11
FactorsaffectingTGA:
FactorsaffectingtheTGcurveThefactorswhichmayaffectthe
TGcurvesareclassifiedintotwomaingroups.:
(1)Instrumentalfactors:
(a)Furnaceheatingrate
(b)Furnaceatmosphere
(2)Samplecharacteristicsincludes:
(a)Weight ofthesample
(b)Sampleparticlesize

12. 12
FactorsaffectingTGA:
1.Instrumentalfactors:
a.FurnaceHeatingrate:Thetemperatureatwhichthe
compound(orsample)decomposedependsupontheheating
rate.Whentheheatingrateishigh,thedecomposition
temperatureisalsohigh.Aheatingrateof3.5°Cperminuteis
usuallyrecommendedforreliableandreproducibleTGA.
b.Furnaceatmosphere:Theatmosphereinsidethefurnace
surroundingthesamplehasaprofoundeffectonthe
decompositiontemperatureofthesample.ApureN2gasfrom
acylinderpassedthroughthefurnacewhichprovidesaninert
atmosphere.

13. 13
FactorsaffectingTGA:
2.Samplecharacteristics:
(a)Weightofthe sample:Asmallweightofthe sampleis
recommendedusingasmallweighteliminatestheexistenceof
temperaturegradientthroughoutthesample.
(b)Particlesizeof the sample:The particlesizeofthesample
shouldbesmallanduniform.Theuseoflargeparticleor
crystalmayresultinapparent,veryrapidweightlossduring
heating.

14. 14
OtherfactorsaffectingTGAcurve:
•Sampleholder
•Heatofreaction
•Compactnessofsample
•Previoushistoryofthesample

15. 15
AdvantagesofTGA:
•Arelativelysmallsetofdataistobetreated.
•Continuousrecordingofweightlossasafunctionof
temperatureensuresEqualweightagetoexaminationoverthe
wholerangeofstudy.
•Asasinglesampleisanalyzedoverthewholerangeof
temperature,thevariationinthevalueofthekinetic
parameters,ifany,willbeindicated.

16. 16
LimitationsofTGA:
•TheChemicalorphysicalchangeswhicharenotaccompanied
bythechangein massonheatingarenotindicatedinthermo-
gravimetricanalysis.
•DuringTGA,Purefusionreaction,crystallinetransition,glass
transition,crystallizationandsolidstatereactionwithno
volatileproductwould notbeindicatedbecausetheyprovide
nochangeinmassofthespecimen.

17. 17
ApplicationsofTGA:
•FromTGA,wecandeterminethepurityandthermalstability
ofbothprimaryandsecondarystandards.
•Determinationofthecompositionofcomplexmixtureand
decompositionof complexORcompositionofcomplex
systems.
•Forstudyingthesublimationbehaviorofvarioussubstances.
•TGAis used to studythekineticsofthereactionrateconstant.

18. 18
ApplicationsofTGA:
•Usedinthestudyofcatalyst:Thechangeinthechemical
statesofthecatalystmaybestudiedbyTGAtechniques.(Zn-
ZnCrO4)Zinc-Zincchromateisusedasthecatalystinthe
synthesisofmethanol.
•Analysisofthedosageforminmedicine.
•Oxidativestabilityofmaterials.
•Estimatedlifetimeofaproduct.

19. 19
ApplicationsofTGA:
•TGAisoftenusedtomeasureresidualsolventsandmoisture,
butcanalsobeusedtodeterminesolubilityofpharmaceutical
materialsinsolvents.
•Theeffectofreactiveorcorrosiveatmosphereonmaterials.
•Moistureandvolatilescontentsonmaterials.

20. 20
References:
•Skoog,DouglasA,FJameshollerandtimothyNiemen,
principlesofinstrumentalanalysis,5
theditionNewYork2001
•InstrumentalmethodsofChemicalanalysis-GURDEEP
R.CHATWAL