Thermal method of analysis

Thermal method of analysis , TGA, DTA, DSC, ppt

1. THERMALMETHODSOFANALYSIS
Mr. Ganesh B. Nigade,
Assistant Professor,
PDEA’s S. G. R. S. College of Pharmacy,
Saswad.
Mob:-9960743549
E mail:[email protected]

2. CONTENTS
Introduction
Types of Different Thermal Analysis
TGA
Principle
Instrumentation
Application
DTA
Principle
Instrumentation
Application
DSC
Principle
Instrumentation
Application
Factor affecting to Thermal analysis
References

3. INTRODUCTION
THERMALANALYSIS–
Techniquesinwhichaphysical(thermal)propertyofa
substanceismeasuredasafunctionof
temperaturewhilethesubstanceissubjectedtoa
controlledtemperaturevariation.
1
THERMAL ANALYSISmeanstheanalysisofa
changeinapropertyofasample,whichisrelated
toanimposedtemperaturealteration.
2

4. Thereisdifferencebetween“thermoanalytical
techniques”and“thermoanalyticalmethods”.
Thetechniquesarecharacterizedbythesuffix
“-metry”,whilethemorecomprehensivemethods,
whichincludetheevaluationandinterpretationof
themeasuredpropertyvalues,areindicatedby
adding“analysis”.
Measurementsareusuallycontinuousandthe
heatingrateisoften,butnotnecessarily,linear
withtime.
Theresultsofsuchmeasurementsarethermal
analysiscurvesandthefeaturesofthesecurves
(peaks,discontinuities,changesofslope,etc.)are
relatedtothermaleventsinthesample.

5. THERMALEVENT

6. When matter is heated, it undergoes
ƒ1) Physical Changes:-Phase change such as melting
Vaporization, crystallization, transition between
crystal structures, change in microstructures in
metal alloy & polymers,
2) Chemical Changes:-iclude reaction to form new
products, oxidation, decomposition, dehydtation,
corrosion

7. TYPESOFDIFFERENTTHERMALANALYSIS
Properties Techniques Methods Abbreviations
Mass Thermogravimetry Thermogravimetric
Analysis
TGA
Pressure Thermomanometry Thermomanometric
Analysis
TMA
Electric PropertiesThermoelectrometry ThermoelectricAnalysisTEA
OpticalPropertiesThermooptometry Thermooptometric
Analysis
TOA
Dimensions or
Mechanical
Properties
Thermomechanometry Thermomechanical
Analysis
TMA
Temperature Thermometry Heating & CoolingCurve
Analysis
--
Temperature
Difference
Differential ThermometryDifferential Thermal
Analysis
DTA
Heat flow
Difference
Differential Scanning
Calorimetry
-- DSC

8. THERMOGRAVIMETRIC ANALYSIS(TGA)
Principle:-
Themassofasampleinacontrolledatmosphereis
recordedcontinuouslyasafunctionoftemperatureor
timeasthetemperatureofthesampleisincreased
(usuallylinearlywithtime).
Measurementsofchangesinsamplemasswithtemperature.
Thetemperatureisincreasedatconstantrateforknowninitial
weightofsubstance&changeinweightarerecordedasfunction
oftemperatureatdifferentintervaloftime.
Notethatmassisameasureoftheamountofmatterinasample,
whereasweightreferstotheeffectofthegravitationalforceona
mass.
Aplotofmassormasspercentageasafunctionoftimeiscalled
athermogramorathermaldecompositioncurve.

9. INSTRUMENTATION
1.Thermobalance
2.Furnace
3.Sample Holder
4.Temperature
measurement
5.Computer-Data
acquisition ,
processing &
control system

10. THERMOBALANCE
The usual range of thermobalance, is from 1 to 1000
mg, with usual sample weighing between 5 to 20
mg.
It provide electronic signal to record the change in
mass.
Types of Thermobalance
1) Null Point type balance
2) Deflection type balance

11. VARIOUSPOSITIONOFBALANCEINFURNACE

12. FURNACE
FurnacesforTGAcovertherangefromambient
temperaturetol000°C,althoughsomecanbeused
fortemperaturesupto1600°C.
Heatingratescanoftenbeselectedfrom0.1°C/min
to100°C/min.
Someunitscanheatasrapidlyas200°C/min.
Insulationandcoolingoftheexteriorofthefurnace
isrequiredtoavoidheattransfertothebalance.
Nitrogenorargonisusuallyusedtopurgethe
furnaceandpreventoxidationofthesample.

13. SAMPLEHOLDER
Samples are typically contained in sample pans
made of platinum, aluminum, or alumina.
Platinum is most often used because of its
inertness and ease of cleaning.

14. TEMPERATURE MEASUREMENT
Thermocouple-
Wires-Platinum,
Rhodium, Chromium, Nickel
Resistance Thermometers-
The electrical resistances of metallic conductors increase with
rising temperature

15. TG CURVE
Type (i) curves: The sample undergoes no
decomposition with loss of volatile
products over the temperature range
shown.
Type (ii) curves: The rapid initial mass-loss
observed is characteristic of desorption
or drying.
Type (iii) curves: represent decomposition of
the sample in a single stage.
Type (iv) curves: indicate multi-stage
decomposition with relatively stable
intermediates.
Type (v) curves: represent multi-stage
decomposition, but in this example stable
intermediates are not formed.
Type (vi) curves: show a gain in mass as a
result of reaction of the sample with the
surrounding atmosphere.
Type (vii) curves: are not often encountered.
The product of an oxidation reaction
decomposes again at higher
temperatures

16. APPLICATIONS
Determination of purity & thermal stability of primary
& secondary standards.
Determination of composition of complex mixture &
decomposition
For study of sublimation behavior of compound
To study reaction kinetics
Determination of Dehydration / Desolvation

17. DIFFERENTIALTHERMALANALYSIS
Principle:-
Differentialthermalanalysis(DTA)isatechniqueinwhich
thedifferenceintemperaturebetweenasubstance
andareferencematerialismeasuredasafunction
oftemperaturewhilethesubstanceandreference
materialaresubjectedtoacontrolledtemperature
program.
Thedifferentialtemperatureisplottedagainsttemperature
ortimeiscalledDTAcurve.
Bothsample&referencematerialheatedincontrolled
condition.
Ifanyreaction(physicalorChemicalchanges)takes
placetemperaturedifference(∆T)willoccurbetween
sample&referencematerial.

18. REFERENCE MATERIAL
The reference material should have the following
characteristics:
(i) It should undergo no thermal events over the
operating temperature range.
(ii) It should not react with the sample holder or
thermocouple,
(iii) Both the thermal conductivity and the heat
capacity of the reference should be similar to those
of the sample.
For inorganic samples-Alumina, and carborundum,
SiC,
For organic compounds-octylphthalate and silicone
oil.

19. INSTRUMENTATION
1.Furnace
2.Sample Holder
3.Temperature
measurement
4.Computer-Data
acquisition ,
processing &
control system

20. FURNACE
Both sample & reference material match thermally
& arranged systematically with the furnace, so that
both are heated or cooled in identical manner.
The metal block surrounding the well act as heat
sink.
Temperature of the heat sink slowly increases by
using internal heater.
Its temperature range from ambient temperature to
l600°C

21. SAMPLEHOLDERS
Sample holder called crucible are made up of
metallic (Aluminum , Platinum) & ceramic (silica).
Sample are usually 1-10 mg for analysis.
The dimension of two crucibles & cell well are as
nearly identical as possible.

22. TEMPERATURE MEASUREMENT
Pair of thermocouples used in DTA.

23. DTA CURVE
TheinitialdecreaseinTisduetotheglass
transition.TheglasstransitiontemperatureTg
isthecharacteristictemperatureatwhich
glassyamorphouspolymersbecomeflexibleor
rubberlike.
Thetwomaximaaretheresultofexothermic
processesinwhichheatisevolvedfromthe
sample,thuscausingitstemperaturetorise.
Whenheatedtoacharacteristictemperature,
manyamorphouspolymersbegintocrystallize
asmicrocrystals,givingoffheatintheprocess.
Crystalformationisresponsibleforthefirst
exothermicpeak
Theminimumlabeled"melting"istheresult
ofanendothermicprocessinwhichheatis
absorbedbytheanalyte.
Thesecondpeakinthefigureisendothermic
andinvolvesmeltingofthemicrocrystals
formedinthcinitialexothermicprocess.The
thirdpeakisexothermicandisencountered
onlyiftheheatingisperformedinthepresence
ofairoroxygen.
Thefinalnegativechangein∆Tresultsfrom
theendothermicdecompositionofthepolymer
toproduceavarietyofproducts.

24. APPLICATIONS
DTA is a widely used tool for studying and characterizing
polymers. The types of physical and chemical changes in
polymeric materials that can be studied by DTA.
DTA is also used in the ceramics and metals industry.
DTA is used to study decomposition temperatures, phase
transitions, melting and crystallization points, and thermal
stability.
An important use of DTA is for the generation of phase
diagrams and the study of phase transitions.
The DTA method also provides a simple and accurate way of
determining the melting, boiling, and decomposition points of
organic compounds.

25. DIFFERENTIALSCANNINGCALORIMETRY
Principle:-
DifferentialScanningCalorimetry(DSC)isaThermal
Analysistechniqueinwhichtheheatflowrate(power)to
thesampleismonitoredagainsttimeortemperature
whilethetemperatureofthesample,inaspecified
atmosphere,isprogrammed.
Itismeasureheatintooroutofsample.
Differencesinheatflowoccurwiththeoccurrenceof
twomajorevents-
1)Theheatcapacityofthesamplewhichincreseswith
temperature
2)Transitionsoccur

26. INSTRUMENTATION
1.Furnace
2.Sample Holder
3.Temperature
measurement
4.Computer-Data
acquisition ,
processing &
control system

27. INSTRUMENTATION
Types of DSC
1) Power-compensated DSC
2) Heat-flux DSC
3) Modulated DSC

28. POWER-COMPENSATEDDSC
Inpower-compensatedDSC,thetemperaturesof
thesampleandreferencearekeptequaltoeach
otherwhilebothtemperaturesareincreasedor
decreasedlinearly.Thepowerneededtomaintain
thesampletemperatureequaltothereference
temperatureismeasured.

29. HEAT-FLUXDSC
Inheat-fluxDSC,thedifferenceinheatflowintothe
sampleandreferenceismeasuredwhilethe
sampletemperatureischangedataconstantrate.
Bothsampleandreferenceareheatedbyasingle
heatingunit.

30. MODULATEDDSC
ModulatedDSC(MDSC)usesthesameheating
andcellarrangementastheheat-fluxDSCmethod.
InMDSC,asinusoidalfunctionissuperimposedon
theoveralltemperatureprogramtoproducea
microheatingandcoolingcycleastheoverall
temperatureissteadilyincreasedordecreased.

31. DSCCURVE

32. APPLICATIONS
GlassTransitionTemperatures:-
DeterminationoftheglasstransitiontemperatureT,isone
ofthemostimportantapplicationsofDSC.Thephysical
propertiesofapolymerundergodramaticchangesat
Tg,wherethematerialgoesfromaglassytoarubbery
state.Attheglasstransition,thepolymerundergoes
changesinvolumeandexpansion,heatflowandheat
capacity.Thechangeinheatcapacityisreadily
measuredbyDSC.
CrystallinityandCrystallizationRate:-
InmostcasesDSCisoneoftheeasiestmethodsfor
determininglevelsofcrystallinity.
ReactionKinetics:-Manychemicalreactions,suchas
polymerformationreactions,areexothermicandreadily
monitoredbyDSCmethods.

33. FACTORAFFECTINGTOTHERMALANALYSIS
Instrumental
1) Furnace Heating rate-↑esheating rate , ↑esdecomposition
2) Furnace atmosphere-pure intertgas like N
2
Sample characteristics
1) Sample particle size
2) Weight of sample

34. REFERENCES
1. Douglas A. Skoog, Principles of Instrumental
Analysis, 6
th
Edition, 894-904.
2. MichaelE.Brown ,Introduction to Thermal Analysis
Techniques and Applications, 2
nd
Edition.
3. Gurdeep Chatwal, Instrumental methods of
chemical analysis : Analytical Chemistry.

35. THANK YOU