Thermal Analysis (DSC,DTA).pptx

Presented by Dhanashree. R. Kavhale... Thermal techniques of Analysis including Differential Scanning Colorimetry, Differential Thermal Analysis.

1. Thermal Techniques Presented by Dhanashree R. Kavhale M. Pharm. (Pharmaceutical Chemistry) Sem- II Department of Pharmaceutical Sciences Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur - 440033

2. Contents Introduction to thermal Techniques Introduction of DSC Principle Instrumentation Applications Introduction of DTA Principle Instrumentation Applications References 2

3. What are Thermal methods of analysis? A group of techniques in which change in physical property of a material is measured as a function of temperature while the substance is subjected to a controlled temperature programme. new materials are studied with respect to – composition, stability, chemical reactions and dynamic properties. These methods also provide information about the structure, composition, purity and the temperature phase change of a material. 3

4. Classification of Thermal Techniques Sr.No. Methods Properties measured 1 Differential scanning calorimetry (DSC) Temperature (∆T) 2 Differential thermal analysis (DTA) Enthalpy 3 Thermal gravimetric analysis (TGA) Reduced mass 4 Dynamic mechanical analysis (DMA) Deformation 5 Dielectric thermal analysis (DTA) Deformation 6 Evolved gas analysis (EGA) Gaseous decomposition 7 Thermal optical analysis (TOA) Optical properties 4

5. Thermal Transitions Low molecular wt. material change their physical state as temperature increases. At. Melting point change, visibly from crystal – liquid. At. B.P. liquid - vapour. Each true phase transition defined thermodynamically, by a marked change in enthalpy, a marked change in enthalpy. These changes in enthalpy can only be determined with methods generally employed to determine transition temperature. 5

6. Differential Scanning Calorimetry (DSC) 6

7. Introduction of DSC A thermal analytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. This technique is used to study what happens to polymers/samples upon heating. The differential scanning calorimeter does all of the above functions and heats the sample with the linear temperature. Both the sample and reference are maintained at nearly the same temperature through out the experiment in DSC. 7

8. Principle It is a technique in which the energy necessary to establish a zero temperature difference between the sample & reference material is measured as a function of temperature. Here, sample & reference material are heated by separate heaters in such a way that their temp are kept equal while these temp. are increased or decreased linearly. During heating two types of reactions can be take place one is the endothermic and the other is the exothermic. 8

9. Exothermic reaction If sample released some amount of heat during phase transition, then reaction is said to be exothermic. In exothermic reaction, less energy needed to maintain zero temp difference between sample & reference. E.g. crystallization, degradation, polymerization. Endothermic reaction If sample absorbs some amount of heat during phase transition then reaction is said to be endothermic. In endothermic reaction more energy needed to maintain zero temp difference between sample & reference. E.g. Melting, boiling, sublimation, vaporization. 9

10. Heat flux DSC The sample and the reference cells are heated at a constant rate and thermocouples are used to detect the temperature difference between sample side and the reference side using single large mass furnace. The large single furnace which acts as an infinite heat sink to provide or absorb heat from the sample. The dynamic sample chamber is the environment of the sample pan compartments and the purge gas. Nitrogen is the most common gas, but alternate inert gas is helium or argon. When using an oxidative atmosphere air or oxygen are the gases of choice. 10

11. Power compensation DSC It directly measures heat flow between sample side and reference side using two separate, low mass furnaces. This individual furnaces use different amount of power to maintain a constant change of temperature between sample and the reference. Platinum resistance thermometers track the temperature variations for the sample and reference cells. Holes in the compartment lids allows the purge gas to enter and contact the sample and reference. 11

12. Instrumentation of DSC 12 Fig: Schematic representation of DSC

13. 1. Heat-flux DSC Sample Holder: Platinum, aluminium, stainless steel. Sensors: Temperature Sensors Usually thermocouples. Furnace: One block for both sample and reference cells. Temperature: The temperature difference between the sample and reference is converted to differential thermal power, which is supplied to the heaters to maintain the temperature of the sample and reference at program value. 13

14. 14 Sample Holder: Platinum, aluminium, stainless steel. Sensors: Pt resistance thermocouple Separate sensors and heaters for the sample and reference sample. Furnace: Separate blocks for sample and reference cells. Temperature: Differential thermal power is supplied to the heaters to maintain the temperature of the sample and reference at the program level. 2. Power Compensated DSC

15. Reference material An inert material like alumina is generally used. An empty pan with lid is also used if the sample weight is small. With sample weight it is necessary to use reference material, because the total weight of the sample and its container should be approximately the same as the total weight of the reference and its containers. The reference material should be selected so that it posses similar thermal characteristics to the sample. Most widely used reference material is alpha alumina Kieselguhr is another reference material normally used when sample has a fibrous nature. 15

16. Sampling Accurately-weigh samples (~3-20 mg) Small sample pans (0.1 mL) of inert or treated metals (AI, Pt, Ni, etc.)Several pan configurations, e.g., open, pinhole, or hermetically-sealed (airtight) pans. The same material and configuration should be used for the sample and the reference. Material should completely cover the bottom of the pan to ensure good thermal contact. Small sample masses and low heating rates increase resolution. 16

17. 17 Fig: Representation of DSC curve

18. Factors affecting DSC curve 1. Instrumental factors Furnace heating rate Furnace atmosphere Sample characteristics Amount of sample Nature of sample Particle size Heat of reaction 18

19. Advantages Rapidity of the determination. Small sample masses. Versatility Simplicity. Applicable study many types of chemical reactions. No of Need calibration over the entire temperature for DSC. Disadvantages Relative low accuracy Not be used for overlapping reactions. Difficulties in test cell preparation in avoiding evaporation of volatile Solvents does not detect gas generation. 19

20. Applications Purity determination of sample directly Detection of polymorphism Quantification of polymorph Detection of meta stable polymorph Detection of isomerism Stability/compatibility studies Percentage crystallinity determination Lyophilisation studies Finger printing Liquid crystals Oxidative stability Safety screening Drug Analysis General chemical analysis Food science Polymers Metals Protein analysis Choosing better solvent 20

21. Differential Thermal Analysis (DTA) 21

22. Introduction of DTA Differential thermal analysis (DTA), is quantitative technique for identifying or analyzing a chemical composition of substances by observing the thermal behavior of a sample as it is heated. The technique is based on the fact that as a substance is heated, it undergoes reactions and phase changes that involve absorption or emission of heat. 22

23. Principle Technique in which the temperature difference between a substance and reference material is measured as a function of temperature, while the substance and reference are subjected to a controlled temperature programme. The Difference in temperature is called as Differential temp(∆t) is plotted against temp. or a function of time. Physical changes usually result in Endothermic peak, whereas chemical reactions those of an oxidative nature are exothermic. Endothermic reaction includes vaporization, sublimation. Exothermic reaction includes oxidation, polymerization, and catalytic reaction. 23

24. Instrumentation Furnace Sample holder Dc amplifier Differential temperature detector Furnace temperature programmer Recorder Control equipment 24

25. 25 Fig: Schematic representation of instrumentation of DTA

26. 1. Furnace In DTA apparatus, one always prefers a tubular furnace. This is constructed with an appropriate material(9-11/30or ribbon) wound on a refractory tube. These are fairly inexpensive. Generally, the choice of the resistance material as well that of refractory is decided from the internal maximum temperature of operation and gaseous environments. 26

27. 2. Sample holders Both metallic as well as non-metallic are employed for the fabrication of sample holders. Metallic materials generally include nickel, stainless steel, platinum and its alloys. Non-metallic material generally includes glass, vitreous silica or sintered alumina. Metallic holders give rise to sharp exotherms and flat endotherms. Non-metallic holders yield relatively sharp endotherms and flat exotherms. 27

28. 3. DC Amplifier It is used for amplification of signals obtained from (T)c. It is gain and low noise circuit. 4. Differential temperature detector In order to control temperature, the three basic elements are required. These are sensor, control element and heater. 28

29. Types of Differential temperature controller On-off control In this device, if the sensor- signal indicates the temperature has become greater than the set point, the heater is immediately cut off. Not used in DTA. Proportional control In on-off controllers there occurs fluctuations of temperature around the set value. These can be minimized if the heat input to the system is progressively reduced as the temperature approaches the desired value. Such a controller that anticipates the approach to the set value is known as proportional controller. 29

30. 5. Furnace temperature programmer/Sensors It provides smooth heating or cooling at a linear rate by changing the voltage through heating component. Modern DTA instruments incorporate electronic temp controller in which the signal from thermocouple in furnace is compared electrically against ref. potential which can be programmed to corresponds to a variety of heating modes & heating rates. 6. Recorder In thermo-analytical studies, the signal obtained from the sensors can be recorded in which the signal trace is produced on paper or film, heating stylus, electric writing or optical beam. 30

31. There are two types of recording devices similar to the TGA. Deflection type Null-point type 7. Control Equipment For some type of samples the atmosphere must be controlled to suppress and undesirable reaction such as oxidation by flowing an inert gas. 31

32. Working of DTA The sample and reference standard are placed in the furnace on flat, highly thermally conductive pans and the thermocouples are physically attached to the pans directly under the sample. This procedure avoids or reduces any thermal lag resulting from the time required for the heat to transfer to the sample and reference materials then to the thermocouples. The thermocouple are connected in opposition. In a similar manner any change in state that involves a latent heat of transition will cause the temperature of the sample to lag or lead that of the reference standard and identify the change of state and the temperature at which it occurred. 32

33. Thermogram A differential thermogram consists of a record of the difference in sample and reference temperature. (∆T)plotted as a function of time t, sample temperature(Ts) reference temperature (Tr) or furnace temperature (Tf). In most of the cases physical changes give rise to endothermic curves whereas chemical reaction gives rise to exothermic. Sharp endothermic - change in crystallinity or fusion. Broad endothermic - dehydration reaction. Exothermic - mostly oxidative reaction. 33

34. 34 Fig: Thermogram

35. Advantages Instruments can be used at very high temperatures. Instruments are highly sensitive. Characteristic transition or reaction temperatures can be accurately determined. Limitations ∆T determined by DTA is not so accurate (2-3 C). Small change in T cannot be determined and quantified. Due to heat variation between sample and reference makes, it less sensitive. 35

36. Applications Qualitative and Quantitative Identification of Minerals: detection of any minerals in a sample. Polymeric Materials: DTA useful for the characterization of polymeric materials in the light of identification of thermo physical, thermo chemical, thermo mechanical and thermo elastic changes or transitions. Measurement of Crystalline: measurement of the mass fraction of crystalline material. 36

37. Continue.. Analysis of Biological Materials: DTA curves are used to date bone remains or to study archaeological materials. 37

38. Reference Instrumental methods of Chemical analysis by G.R. Chatwal. 38

39. Thank you.. 39