differential thermal analysis explained.pdf

DTA

1. DIFFERENTIAL THERMAL
ANALYSIS (DTA)
Presented By
Mahpara Gondal
Senior Lecturer
Rashid Latif college of pharmacy

2. Thermal Analysis Techniques
•Whenamaterialisheateditsstructuraland
chemicalcompositioncanundergochanges
suchasfusion,melting,crystallization,
oxidation,decomposition, transition,
expansionandsintering.
•UsingThermalAnalysissuchchangescanbe
monitoredineveryatmosphereofinterest.The
obtainedinformationisveryusefulinboth
qualitycontrolandproblemsolving.

3. Types of thermal analysis
•TG (Thermogravimetric) analysis:
weight
•DTA (Differential Thermal Analysis):
temperature
•DSC (Differential ScanningCalorimetry):
temperature

4. •InDifferentialThermalAnalysis,the
temperaturedifferencethatdevelops
betweenasampleandaninertreference
materialismeasured,whenbotharesubjected
toidenticalheat-treatments.
•TherelatedtechniqueofDifferentialScanning
Calorimetryreliesondifferencesinenergy
requiredtomaintainthesampleandreference
atanidenticaltemperature.

5. Thermogravimetry (TG)
•Thermogravimetryisthemeasurementofthe
massofasampleasthetemperatureincreases.
Thismethodisusefulfordeterminingsample
purityandwater,carbonate,andorganic
content;andforstudyingdecomposition
reactions.

6. INTRODUCTION
•Thisisacomparisonmethod
•Analyticalmethodforrecordingthe
differenceintemperature(∆T)b/wa
substanceandaninertreferencematerialas
afunctionoftemperatureortime
•Anytransformation–changeinspecificheat
oranenthaplyoftransitioncanbedetected
byDTA

7. •InDTAbothtestsample&aninertreference
material(alumina)–controlledheatingor
coolingprogramming
•Ifzerotemperaturedifferenceb/wsample&
referencematerial–sampledoesnot
undergoanychemicalorphysicalchange.
•Ifanyreactiontakesplacetemperature
difference(∆T)willoccurb/wsample&
referencematerial

8. •ADTAcurvecanbeusedasafingerprintfor
identificationpurposes,forexample,
•inthestudyofclayswherethestructural
similarityofdifferentformsrendersdiffraction
experimentsdifficulttointerpret.

9. PRINCIPLE
•TheprincipleofDTAisbasedonthefactthat
thethermaleffectsassociatedwiththephysical
andchemicalchangesaremeasuredbya
differentialmethodinwhichthesample
temperatureiscontinuouslycomparedagainst
thetemperatureofthethermallyinertreference
material.thisdifferenceintemperature,called
differentialtemperature T,isrecordedas
afunctionofreferencematerialtemperatureor
furnacetemperature.

10. DTA CURVE/ THERMOGRAM
•Thedifferentialtemperatureisthenplotted
againsttimeoragainsttemperature.
•DTAcurveprovidesdataonthetransformations
thathaveoccurred,suchasglasstransitions,
crystallization,meltingandsublimation.Thearea
underaDTApeakistheenthalpychangeandis
notaffectedbytheheatcapacityofthesample.

11. ∆T VS Temp.
Sharp Endothermic–changes in crystallanityor fusion
Broad endotherms-dehydration reaction
Physical changes usually result in endothermic curves
Chemical reactions are exothermic

12. Cont..
•ENDOTHERMIC PEAK:anendothermic
peak,isapeakwherethetempofthesample
fallsbelowthatofthereferencematerial,i.e.,
Tisnegative
•EXOTHERMIC PEAK:anexothermicpeak,
isapeakwherethetemperatureofthe
samplerisesabovethatofthereference
material,i.e.,Tispositive.

13. Apparatus
•The key features of a differential thermal
analysis kit are as follows
1. Sample holder comprising thermocouples,
sample containers and a ceramic or metallic
block.
2. Furnace.
3. Temperature programmer.
4. Recording system.

17. CONTAINERS:
•Variouscontainershavebeenusedtocontainsampleandreference
material.Theyareusuallymadeofalumina,borosilicate,fused
quartz,stainlesssteel,nickel,platinumgraphiteetc.Thechoiceof
materialdependsonthesampleandtemperaturerangetobestudied.
Thereshouldbenoreactionbetweensampleandcontainerduring
pyrolysis.
•THERMOCOUPLE :Themostcommonlyusedtemperaturedetecting
deviceisthethermocouplewhichisconstructedfromChromelvs
alumel,Coppervsplatinum,10-15%rhodiumandothers.
•Thechoiceofthermocoupledependsonthemaximumtemperature
desired,chemicalreactivityofsampleandsensitivityofd.camplifier.
•Fortempupto1500C,aplatinumcoupleissatisfactory,forfairlylowtemp
(upto300C)coppercoupleisrecommendedandfortempupto1100C
chromel-alumelissuitable

18. ….
•FURNACE:Thechoiceoffurnacegeometryalsodependson
thetemperaturerangtobestudied.Thefurnacewhichcovers
therangeof190Cto2800Chavebeeninuse.
•The temperature rise of the furnace is usually controlled by
either increasing the voltage through the heater element by a
motor driven transformer. The most commonly used rate is 10
0
to 15
o
per min.
•AMPLIFIER:A good low noise-level d.camplifiers are used as
differential temp detectors.
•RECORDER: Strip chart recorders or galvanometric recorders
or an X-Y recorders are used to record amplified T signals as a
function of time or temp

19. WORKING
•A furnace is used which contains a sample holder or sample
block, the latter of which has two identification and symmetrically
located chambers.
•The sample is loaded into a crucible, which is then inserted into
the sample well (S). A reference sample is made by placing a
similar quantity of inert material in second crucible marked as R.
The weight of S and R equal.
•One set of thermocouple is inserted into the inert material, such as
aluminiumoxide and the other set of thermocouple junction is
placed in other chamber containing sample. Some other
temperature detecting devices are also employed.
•The metal block surrounding the wells acts as a heat sink. The
temp of the sink is slowly increased using an internal heater. The
sink in turn simultaneously heats the sample and reference
material.

20. Cont..
•Theoutputofdifferentialthermocouple,T
s-T
risamplifiedand
sendtodataacquisitionsystem.Asthetemperatureis
increased,therewillbeabriefdeflectionofthevoltmeterifthe
sampleisundergoingaphasetransition.
•Ifthereisnodifferenceintemp,nosignalisgenerated,even
thoughtheactualtempofbothsampleandreferenceareboth
increasing
•Thesampleandblocktemperaturearethenincreasedatlinear
rate,andthetemperaturebetweensampleandreference
materialsiscontinuouslymeasuredorrecordedagainstthe
furnaceorreferencematerialtemperature.

21. •Heart of the analysis –heating block
(Summary)
•Identical pair of cavities for the sample, ref.
material
•Whole unit is set in an oven-control pressure
•Thermocouple is place directly in contact with
the sample and another in contact with the
reference
•Temp.ofthe block is raised, the temperature of
the sample & reference follow
•Zero temp. difference –no physical or chemical
change
•If any reaction –difference in ∆T

22. Suppose the sample temp and differential temp is
compared with each other as a function of time, then
the curve will be like:

23. Cont..
•AtpointA,ithasbeenassumedthatsampleundergoes
sometypeofendothermicreaction.Itisalsoseenthat
thesampletempisnolongerlinearw.r.t.timebutlacks
thefurnacetempasaresultofabsorptionofheat.
•ThereactionwillcompleteatB,andsampletemp
increasesandaftersometimeitbecomesequalto
furnacetempagainatC.duringactualtransitionwhen
beginsatAthesampleandreferencetempdiffersideally
incaseofpeakABC,withamaximumatB.beyondA,
curvereturnstobaselineT=0duetoequalizationof
sampleandreferencetemp.

26. Differential Thermal Analysis
advantages:
•instrumentscanbeusedatveryhigh
temperatures
•instrumentsarehighlysensitive
•characteristictransitionorreaction
temperaturescanbeaccurately
determined
disadvantages:
•uncertaintyofheatsoffusion,transition,
orreactionestimationsis20-50%
DTA

27. Factors affect results in DTA
•Sample weight
•Particle size
•Heating rate
•Atmospheric conditions
•Conditions of sample packing into dishes

29. Applications
•Quantitative identification and purity
assessment of materials are accomplished by
comparing the DTA curve of sample to that of
a reference curve
•Impurities may be detected by depression of
the M.P

30. Cont…
•A DTA curve cant be identical for 2 substances so it
can be used only as afinger printfor identification
purposes.
•As M.P can be easily determined by DTA, so this
technique can be used to check purity of sample.
•determination of phase diagrams, heat change
measurements and decomposition in various
atmospheres, thermal stabilities.
•Measuring moisture content of powdered
substances

31. Cont..
•As the area of peak of DTA curve is directly
proportional to the total heat of reaction and
hence to weight of sample so quantitative
analysis is possible.
•Used to identify polymers, fats , amino acids,
proteins, metal and non-metal oxides
•Thermogramof typical explosives and
propellants provide useful information
regarding the manufacture, storage and
application of these high-energy materials.