1. Dnyanasadhana College, Thane.
hhh
Department of Chemistry T.Y.B.Sc. Analytical Chemistry Paper-IV Sem-VI
DIFFERENTIAL THERMAL analysis
Dr.Bhagure G.R.

2. Contents 4.1.3 Differential Thermal Analysis (DTA): Principle,
Instrumentation –balance,
Thermocouple
Reference material used in TA (MgO,Al2O3,SiC),
DTA curve
Applications : DTA of CaC2O4.H2O and CuSO4.5H2O, Difference between TGA and DTA.

3. A graph of ∆T Vs. temperature is plotted
DTA is a technique in which the temperature difference between the sample and the reference material (thermally inert ) is continuously recorded as a function of temperature or time.
The sample and reference material are subjected to a controlled temperature programme
A graph of ∆T Vs. temperature is plotted

4. Principle of DTA
When a graph of ∆T Vs. temperature is plotted, the maxima and / or minima due to exothermic and/ or endothermic processes.
Maxima and minima are called as peaks.
Maxima = exothermic process in which heat is evolved from the sample causing temperature to increase.
Minima = endothermic process in which heat is absorbed by the sample causing temperature to decrease.

5. Peak area (A) is corrected to the mass of the analyte (m) as
A = K G m ∆ H =
K’ m ∆ H
G = calibration factor related to sample geometry
K = constant related to thermal conductivity of sample
K’ = constant related to heating rate, particle size, placement of sample etc.
The mass of a particular analyte can be determined if K’ and ∆ H can be known by calibration.

6. Solid–solid phase transitions
Endothermic
MELTING
Vaporization
Boiling
Desolvation
Solid–solid phase transitions
Chemical degradation

7. Oxidative decomposition
EXOTHERMIC REACTIONS
Crystallization
Oxidative decomposition
Solid state reactions
Chemisorption

8. DIFFERENTIAL THERMAL ANALYSER
Instrumentation
1.Sample holder
2.Furnace.
3.Temperature programmer
4.Recording system

9. SCHEMATIC DIAGRAM OF DTA INSTRUMENT

12. 2.Furnace or heating device
The sample holder assembly consists of a thermocouple each for the sample and reference, surrounded by a block to ensure an even heat distribution.
sample containers made from ceramic or metallic block.
1.Sample holder
Furnace consist of electrical heating systems. Electrical heating coils are made from Nichrome wire windings & platinum wire windings.
Furnace should provide uniform hot & linear heating rate one
Should have cooling facility for rapid return to ambient temperature
2.Furnace
or heating device

13. Thermocouple are used as temperature sensors.
Thermocouples are made from Chromel P Alumel wires (both made of Nickel-chromium alloys) are used to measure temperature upto 11000C.
Thermocouples are made of pure Platinum and Platinum-Rhodium are used to measure temperature above 11000C.
While selecting thermocouples as temperature sensors, the following points should be consider,
Temperature interval
Thermoelectric coefficient
Chemical compatibility with the sample
Chemical gaseous environment
Reproducibility
Availability
Cost
3. THERMOCOUPLES

14. 4.Differntial Temperature Detector
The thermocouples served as the temperature sensor .The voltage signal produced dependence on the temperature different, ∆T between two junctions of the thermocouples
4.Differntial Temperature Detector
It Consist of an amplifier to magnify signals coming from temperature sensor (T) & differential temperature sensor (∆T) of the thermocouples
5.Recorder

15. 6.Atmpospheric Control & Cooling Controls:
A Facility for flushing the sample & reference assembly with selected gas is provided.
There is also cooling facility to cool the assembly to ambient temperature .
Liquid Nitrogen is used in a special low temperature assembly.
6.Atmpospheric Control & Cooling Controls:

16. Reference material used in DTA (MgO,Al2O3,SiC

17. Characteristic of the Reference material used in DTA
Should not under go thermal events over the operating temperature
It should be inert towards sample holder or thermocouple
Thermal conductivity & het capacity should be similar to that of sample

18. Factors affecting DTA curve Sample characteristics
2. Instrumental characteristics
3.Environmentl factors

19. Sample characteristics
Amount of Sample:
Small size sample give best peak which can be easy for resolution.
Particle size:
Finely powdered sample size sample give best peak. Particles having bigger size increases the peak area.
Sample packing:
It is regular practice to mix Sample with inert material like glass like alumina. The degree of crystallinity of sample and compactness also affect on DTA curve.

20. Instrumental characteristics
Sample holder
Sample holders made up from high thermal conducting material gives sharp exothermic peak but relatively flat endothermic peak.
Generally very small sample holders made from glass or ceramic re used. Sometimes shallow metallic pans are used.
Thermocouples:
Position of Thermocouples affect on DTA curve.
If Position of Thermocouples is not varies reproducible results can be obtained
Furnace characteristics: The type of winding on furnace shows direct effect on DTA curve.
The grooved muffled core furnace are preferred because it gives uniformity in windings.
Heating rate:
Heating rate has great influence on DTA curve. Generally ,heating rate of 100c to 200c is preferred for sharper peak .
Recorder:
DTA curve also effect by type, chart speed, and pen response of recorder.

21. 3.Environmentl factors
Static gaseous atmosphere: Studies in Static gaseous atmosphere are not precise.
Dynamic gaseous atmosphere: The results obtained in Dynamic gaseous atmosphere re more precise & accurate

22. Qualitative analysis
Clay
Reaction products

23. Quantitative analysis
DTA peaks re proportional to total het of reaction which is equivalent to wt. of the sample
Analysis of Polymers
Ceramic & metal Industry
Phase transitions Ex.Sulphur

24. DTA Curves

25. DTA curve of CaC2O4.H2O in the presence of O2. Heating rate = 80C/min

26. Calcium oxalate monohydrates gives two endotherms
CaC2O4.H20CaC2O4 +H20 1.
Around
200 Oc
CaCO3.CaO +C02 2.
800 Oc

27. Calcium oxalate monohydrates gives one exotherms
2CaC2O4O+O2CaCO3+CO2
(In Air) 1.
Intermediate
Exotherm
In Nitrogen atmosphere the above process is endothermic

28. DTA curve of CuSO4.5H2O in the presence of O2. Heating rate = 80C/min

29. DTA curve of CuSO4.5H2O gives three endotherms
CuSO4.5H2O CuSO4.3H2O 1.
81-96 Oc
CuSO4.3H2OCuSO4.2H2O 2. Oc
CuSO4.2H2OCuSO4.H2O 3. Oc

30. DIFFERENCE BETWEEN TGA & DTA
Change in mass of sample with increase in temperature
Plots a graph of change in mass Vs. T
Change in mass gives information about
Change in sample composition
Change in thermal stability
Change in kinetic parameter
Measure the temperature difference between sample and reference with increase in temperature.
Plots a graph of ∆T Vs. T
maxima and minima gives information about exothermic and endothermic processes associated with sample

31. Instruments can be used at very high temperatures
Advantages
Instruments can be used at very high temperatures
Instruments are highly sensitive
Characteristic transition or reaction temperatures can be accurately determined.