Differential Thermal Analysis (DTA)

DTA: Introduction, Principle, Instrumentation, Application

1. Differential Thermal Analysis (DTA) Presented by: Shobhit Srivastava M.Pharm 1 st year Presented to: Dr. Sujeet Kumar Gupta Associate Professor Hygia Institute of Pharmaceutical Education & Research, Lucknow

2. Content Thermal analysis Methods of Thermal Analysis Differential thermal analysis Introduction Principle Instrumentation Factor affecting curve of DTA Advantage Disadvantage Application

3. Thermal Analysis Thermal analysis is defined as “series of techniques for measuring the temperature dependency of a physical property of a certain substance while varying the temperature of the substance according to a specific program.” The substance referred to here includes reaction product. Physical properties include adsorption, sublimation, evaporation, desorption etc. whereas chemical properties include oxidation/reduction, crystallization, loss on drying etc.

4. Methods of T hermal Analysis TG ( Thermogravimetric ) analysis: Technique where by the weight of a substance, in an environment heated or cooled at a controlled rate, is recorded as a function of time or temperature. DTA (Differential Thermal Analysis ): Technique involve recording of difference in temperature between a sample and reference material against either time or temperature as the two specimens are subjected to identical temperature regimen in an environment heated or cooled at a controlled rate.

5. DSC (Differential S canning Colorimetry ): Technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of time.

6. Differential Thermal Analysis (DTA) Introduction Differential thermal analysis ( DTA) is a thermo analytical technique similar to differential scanning calorimetric . In DTA ,the material under study and an inert reference are made to undergo identical thermal cycles, while recording any temperature difference between sample and reference. This differential temperature is then plotted again time or against temperature. The curve plotted is called as DTA curve or thermogram .

7. Changes in the sample either endothermic or exothermic, can be detected relative to the inert reference . Thus a DTA curve provides data on the transformation that have occurred such as glass transition, crystallization , melting and sublimation. The area under DTA peak is the enthalpy change and is not affected by the heat capacity of the sample. In DTA both the test sample and inert reference material (alumina) controlled heating or cooling programming. If zero temperature difference between sample and reference material – then sample doe not undergo any chemical and physical changes . If any reaction takes place temperature difference will occur between sample and reference material.

8. Fig 1.Differential thermogram showing types of changes encountered with polymeric materials. + Exothermic ∆T Endothermic Exothermic T g Glass transition Melting Crystallization Oxidation No Oxidation Decomposition Temperature

9. Principle Monitoring of the temperature difference between a sample and an inert reference as they are heated uniformly. Endothermic or Exothermic changes in the sample lead to characteristic deviation in temperature which can be used for qualitative and quantitative analysis. A technique in which the temperature difference(∆T) between a substance and reference material is measured as function of temperature , while the substance and reference are subjected to controlled temperature programmed. The difference in the temperature is called as differential temperature and is plotted against temperature or function of time .

10. Physical changes usually result in endothermic peaks, whereas chemical reaction those of an oxidative nature show exothermic peak . Endothermic reaction ( absorption of heat) includes sublimation and gives downward peak . Exothermic reaction ( liberation of heat) includes oxidation, polymerization and gives upward peak.

11. Instrumentation A Differential Thermal Analysis consists of: 1 . Sample holder 2 . Thermocouples 3 . F urnace 4 . T emperature P rogrammer 5 . R ecording system The key feature is the existence of two thermocouples connected to a voltmeter. One thermocouple is placed in an inert material such as aluminum oxide, while the other is placed in a sample of the material under study. Fig 2. Block Diagram of DTA

12. Fig 3. Schematic diagram of a typical instrument for DTA.

13. Sample holder: Material: Low cost, ease of fabrication, inertness Metallic (e.g. Nickel, steel, Platinum  ) Non metallic (e.g. glass, silica, alumina) (b) Geometry: Ideal spherical but due t o fabrication problem cylindrically geometry is used.

14. 2. Furnace: Prefer a tubular furnace (wire or ribbon). Desired temperature regulation and programming. Inexpensive. Dimension, which depend mainly upon the length of the uniform temperature zone. Made of Tungsten, Chromel , Nichrome v, Silicon carbide etc. Where, P = Power L = Length Km = Thermal conductivity coefficient d 1 = Diameter of heater coil round on the ceramic d 2 = Diameter of furnace cell T 1 & T 2 = temperature of heating element & surface temperature of furnace shell

15. 3. Temperature controller: (a) Temperature controller: Sensor Control element (rate of heat input require to match the heat loss from the system) Heater There are 2 methods for controlling temperature: On-off control: If temperature greater than the set point then heater cut off (not used in DTA). Proportional control: Proportionally reduced the temperature if temperature reached to desired value (used in DTA). (b) Temperature programming: Time dependent temperature cycling of the furnace.(maintain constant temperature)

16. 4. Temperature Recorder: Single trace is produce on paper or film, by ink, heating stylus, electric writing or optical beam. 2 types of recorder are used in DTA: (a) Deflection type: Pointer moved by input single (1) Beam (2) Cantilever (3) Spring (4) Torsion Fig 4.Types of deflection recorder

17. (b) Null type: Input single is compared by the reference signal and the difference is amplified. 5. Thermocouple: Temperature sensor are thermocouple. Made by Chromel & Alumel wire.

18. Factors affecting curve of Differential Thermal Analysis There are so many factors that affects the DTA curve . They are divided into two SAMPLE CHARACTRISTIC INSTRUMENTAL FACTOR

19. Table 1. Factor and their effect Factor Effect Suggestions 1. Heating rate Change in the peak size and position Use allow heating rat 2. Location of Thermocouple Irreproducible curve Standardize thermocouple location 3. Atmosphere around the sample Change in the curve Inert gas should be allowed to flow 4. Amount of sample Change in the peak size and position Standardize sample mass 5. Particle size of Sample Irreproducible curve Use small uniform particle 6. Packing density Irreproducible curve Standardize packing techniques 7.Sample container Change in peak Standardize container

20. Advantages: Instruments can be used at a very high temperature. Instruments are highly sensitive. Flexibility in crucible volume/form. Characteristic transition or reaction temperature can be accurately determined. Disadvantages : Reaction or transition estimations is only 20% to 50% DTA. Uncertainty in heats of fusion.

21. Application of Thermal Differential Analysis Qualitative and Quantitative identification of Minerals : Detection of any minerals in sample. Polymeric materials : DTA is useful for characterization of polymeric materials in the light of identification of thermo-physical, thermo-chemical, thermo-mechanical, and thermo-elastic changes or transition. Measurement of crystalline: Measurement of the mass fraction of crystalline material in semi- crystalline polymer.

22. Producing phase diagrams and identifying phase conversions. Finding the change in enthalpy (ΔH) in the entire procedure. Fingerprinting of certain materials. Verifying decomposition temperatures of various organic composites. Exemplifying inorganic compounds. Analyzing a physical mixture of commercial polymers qualitatively. Quantitative identification and purity assessment of material are accomplished by comparing the DTA curve of sample to that of a reference curve. Impurities may be detected by depression of the melting point.

23. DTA is widely used in the pharmaceutical and food industries. DTA may be used in cement chemistry mineralogical research and in environmental studies. DTA curves may also be used to date bone remains or to study archaeological materials Using DTA one can obtain liquids & solidus lines of phase diagrams .

24. Reference: Skoog Douglas A., Holler James F., Crouch Stanley R., “Instrumental Analysis”, Indian edition, 2007, published by Cengage lerning india pvt. Ltd., New Delhi, page no.980-82. Braun Robert D., “Introduction to Instrumental Analysis”,2004, published by PharmMed Press, Hyderabad, page no.939-40. Chatwal GR, Anand SK. Instrumental method of chemical analysis. 5th ed. Mumbai: Himalaya publishing house; 2007. p. 2.719-2.738.

25. Thank you !!