1. By: z. mohammadpour

2. Types of thermal analysis TG (Thermo Gravimetric) analysis: weight DTA (Differential Thermal Analysis): temperature DSC (Differential Scanning Calorimetry): energy 2 3. Differential Thermal Analysis (DTA) Introduction: Differential thermal analysis is a technique in which the difference in temperature between a substance and reference material is measured as a function of temperature while the sample and reference are subjected to controlled temperature programme. 3 4. Phenomena causing changes in temperature Physical: Adsorption (exothermic) Desorption (endothermic) A change in crystal structure (endo or exothermic) Crystallization (exothermic) Melting (endothermic) Vaporization (endothermic) Sublimation (endothermic) 4 5. Chemical: Oxidation (exothermic) Reduction (endothermic) Break down reactions (endo or exothermic) Chemisorption (exothermic) Solid state reactions (endo or exothermic) 5 6. 6 7. Comparison between TA & DTA 7 8. Historical aspects: In 1899 Robert Austen improved this technique by introducing two thermocouples, one placed in sample and other in the reference block. This technique was later on modified by Burgess(1909), Norton(1939), Grim(1951), Kerr(1948), Kauffman(1950), Fold Vari(1958). 8 9. DTA systems: 9 10. Instrumentation: 10 11. 11 12. 2. Furnace Assembly 12 13. 3. Temperature programmer 4. Amplifier and recorder 13 14. Theoretical Aspects 1. Speil theory m(H)/gk= 1 2 14 15. 2. Boersma equation I. Cylinder geometry 1 2 = 2 4 II. Spherical geometry 1 2 = 2 6 15 16. III. Flat plate geometry 1 2 = 2 2 IV. Large ceramic block 1 2 = 2 6 2 + 1 16 17. V. Metal cups 1 2 = 17 18. 3. Pacor expression 1 = 2 1 = 2 + 1 2 1 2 1 = = 2 18 19. 4. Gray general theory = + R + I II III 19 20. 20 21. Factors affecting DTA curves: DTA is a dynamic temperature technique. Therefore, a large number of factors can affect. These factors can be divided into the two groups: i) Instrumental factors ii) Sample factors 21 22. Instrumental factors : Furnace atmosphere Furnace size and shape Sample holder material Sample holder geometry Wire and bead size of thermocouple junction Heating rate Speed and response of recording instrument Thermocouple location in sample 22 23. Sample characteristic : Particle size Thermal conductivity Heat capacity Packing density Swelling or shrinkage of sample Amount of sample Effect of diluent Degree of crystallinity 23 24. Heating rate 2 1 = Heating rate 24 25. Heating rate 25 26. Effect of heating rate on curve peak resolution, compound used was cholesterol propionate. 26 27. Effect of heating rate on the peak amplitude, compound used was cholesterol propionate. 27 28. Furnace atmosphere + An approximation form of Vant Hoff equation: 2 1 = 2 1 = 2 1 2 1 28 29. Generally two types of gaseous atmosphere are employed: a. A static gaseous atmosphere b. A dynamic gaseous atmosphere 29 30. Effect of O2 and N2 atmosphere on the DTA curve of a mixture of 2.5% lignite in Al2O3. 30 31. Effect of atmosphere on the thermal decomposition of SrCO3. 1 927 2 31 32. Sample holder Effect of sample holder diffusivity on the shape of the DTA peak. 32 33. Low thermal conductivity material Endothermic High thermal conductivity material Exothermic Ceramic holders & Metal holders 33 34. Comparison of block and isolated container sample holders advantages disadvantages Block type 1. Good temperature uniformity 2. Good thermal equilibration 3. Good resolution 4. God for b.p. determinations 1. Poor exchange with atmosphere 2. Poor calorimetric precision 3. Difficult sample manipulation 4. Sensitive to sample density change Isolated container type 1. Good exchange with atmosphere 2. Good calorimetric precision 3. Good for high temperature use 1. Poor resolution 34 35. Thermocouples = 1 2 0dt 1 2 0 dt = 2 6 . 1 + 35 36. Thermocouple location 36 37. Effect of having an asymmetric arrangement of sample and reference thermocouples (a) Thermocouple 0.06 cm from center of sample (b) Thermocouple 0.3 cm from center of sample 37 38. System temperature versus T for carborundum in both cells 38 39. Sample mass 2 = 39 Sample mass 40. Sample particle size 40 41. DTA curve of silver nitrate (a) Original sample (b) The slightly ground sample (c) The finely ground sample 41 42. Effect of diluent Masking effect of sample peaks caused by diluent (a) 8-quinolonol diluted to 6.9% with carborundum (b) 8-quinolinol diluted to 5.9% with alumina 42 43. Key operational parameters 43 44. Factors that influence DTA curve 44 45. Peak area provide quantitative information regarding the mass of the sample = Calibration = Heat of transition Chart speed 45 46. Calibration standards 46 47. Differential Scanning Calorimetery (DSC) DSC measures differences in the amount of heat required to increase the temperature of a sample and a reference as a function of temperature 47 48. Control loupes in DSC sample reference Differential temperature control loop to maintain temperature of the two pan holders always identical Average temperature control loop to give predetermined rate of temperature increase or decrease 48 49. Power compensated DSC: Temperature differences between the sample and reference are compensated for by varying the heat required to keep both pans at the same temperature. The energy difference is plotted as a function of sample temperature. 49 Platinum sensors Sample heater Reference heater 50. Heat flux DSC utilizes a single furnace. Heat flow into both sample and reference material via an electrically heated constantan thermoelectric disk and is proportional to the difference in output of the two thermocouple junctions. 50 51. Differential Scanning Calorimetry PET -1.5 -1 -0.5 0 0.5 1 1.5 2 0 50 100 150 200 250 300 350 Temperature (C) HeatFlow(W/gm) Melting Glass Transition Crystallization ENDOTHERMIC EXOTHERMIC Sample: Polyethylene terephthalate (PET) Temperature increase rate: 20C/min Temperature range: 30C - 300C 51 52. Quantitative DSC: = 52 Independent of temperature 53. 6 Influence of Sample Mass Temperature (C) 150 152 154 156 0 -2 -4 -6 DSCHeatFlow(W/g) 10mg 4.0mg 15mg 1.7mg 1.0mg 0.6mg Indium at 10C/minute Normalized Data 158 160 162 164 166 Onset not influenced by mass 53 54. 6 Effect of Heating Rate on Indium Melting Temperature 154 156 158 160 162 164 166 168 170 -5 -4 -3 -2 -1 0 1 Temperature (C) HeatFlow(W/g) heating rates = 2, 5, 10, 20C/min 54 55. 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 55 56. Disadvantages: Relative low accuracy and precision (5-10 %) Not be used for overlapping reactions Need calibration over the entire temperature for DTA 56 57. References: P. J. Elving & I. M. Kolthoff, Chemical analysis, Vol. 19, P134, 1964. H. Faghihian, S. Shahrokhian, H. Kazemian, thermal methods of analysis, P81, 2006. G. klancnik, J.Medved, P. Mrvar., Materials and Geoenvironment, Vol. 57, No. 1, pp. 127142, 2010. 57 58. ? 58