Dta

1. THERMAL ANALYSIS By T.shivakumar B .Pharmacy [email protected]

2. Content… Thermal methods of Analysis Types – Introduction Special emphasis on Differential Thermal Analysis Differential Scanning Calorimetry Theory, Instrumentation, Methodology, Applications.

3. Thermal methods of Analysis This is based on the concept of heating a sample – followed by well-defined modified procedures, such as : gravimetric analysis, differential analysis and titrimetric analysis. Some property of a system is measured as a function of temperature. Thermal spectra or Thermograms

4. Conti…. Thermo grams characterize a single or multi component system in terms of : Thermodynamic properties , and physicochemical reaction kinetics .

5. Thermal Analysis is widely used …

6. Different Techniques Thermometric Titration (TT) Thermal Mechanical Analysis (TMA) Dynamic Mechanical Analysis (DMA) Differential Scanning Calorimetriy (DSC) Thermal Gravimetric Analysis (TGA) Differential Thermal Analysis (DTA) Temperature Programmed Desorption (TPD)

7. Principle Sample is heated at a constant heating rate Sample’s Property Measured Wt TGA Size TMA Heat Flow DSC Temp. DTA Heat of mixing TT Tem. at which TPD gas is desorbed at the surface.

8. What is DTA ? Involves the technique of recording the difference in temperature between the Test and Reference material time being constant for both. Hence the Differential Thermogram consists record of difference in Temperatures.

9. Thermogram A differential thermogram consists of a record of the difference in sample and reference themperature (∆T) plotted as a function of time t, sample temperature(T s ), reference temperature( T r ) or furnace temperature( T f ). In most of the cases, physical changes give rise to endothermic curves, whereas chemical reactions give rise to exothermic peaks .

10. Factors affecting DTA curve A] Environmental factors B] Instrumental factors i ] Sample holder ii] Differential temperature sensing device iii] Furnace characteristics iv] Temperature- programmer controller v] Thermal Regime vi] Recorder C] Sample factors 1] Physical 2] Chemical

11. Instrumentation A differential thermal analyzer is composed of five basic components, namely : 1} Furnace 2} Sample holder 3} temperature controller and recorder 4} thermocouple 5} Cooling device

12. 1} Furnace Tubular furnace is most commonly used because it possess the desired characteristic for good temperature regulation and programming. Dimension of the furnace is depends upon the length of the uniform temperature zone desired.  The choice of resistance material is depends on the maximum temperature of the operation and gaseous environment. Grooved muffled cores preferred.

13. 2} Sample holder Should having low cost, ease of fabrication and inertness towards the sample. Metallic material : nickel, stainless steel, platinum Non-metallic material : glass, vitreous silica or sintered alumina. Most commonly the shape of holder is cylindrical . The nature of physical constant between the sample, thermocouple junction and the specimen holder affect the DTA signals. So to maintain it, a sample holder with dimples in which thermocouple junctions are inserted (thermocouple wells) are used.

14. 3} Temperature controller and recorder A] Temperature Controller  In order to control temperature, the three basic elements are required. These are sensor, control element and heater . The control element governs the rate of heat-input required to match the heat loss from the system. The location of sensor with respect to the heater and mode of heat transfer measure the time elapsed between sensing and variation in heat input.

15. Conti… B] Temperature programming It transmits a certain time-based instruction to the control unit. By this device one can achieve linearity in the rate of heating or cooling it is driven in a non-linear fashion using a special cam-drive. Heating rates of 10-20 o C / mints are employed. C] Recorder The signals obtained from the sensors can be recorded in which the signal trace is produced on paper or film, by ink, heating stylus, electric writing or optical beam.

16. 4} Thermocouple Thermocouples are the temperature sensors. It is made up from chromel p and alumel wires are used to measure and control temperature up to 1100 C in air. For above 1100 C one should use thermocouple made from pure platinum & platinum-rhodium alloy wires.

17. 5} Cooling device It is separate from the temperature programmer because it is independent from heating .

18. DTA Analyzer

19. Methodology Insert a very thin thermocouple into a disposable sample tube 2 mm in diameter and containing 0.1- 10 mg of sample, Another identical tube is either kept empty or filled with a reference substance, such as quartz, sand, alumina. The two tubes are simultaneously inserted into the sample block and subsequently heated (or cooled) at a uniform predetermined programmed rate

20. Requirements DTA—A few of the vital aspects are : Pre-treatment of the specimen, Particle size and packing of the specimen, Dilution of the specimen, Nature of the inert diluent , Crystalline substances must be powdered, and sieved through 100-mesh sieve

21. Cont… Either to suppress an unwanted reaction (e.g., oxidation), or to explore the study of a reaction(e.g., gaseous reaction product)—the atmosphere should be controlled adequately.

22. DTA Curve

23. Advantages : Instruments can be used at very high temperatures. instruments are highly sensitive. flexibility in crucible volume/form. characteristic transition or reaction temperatures can be accurately determined. Disadvantage: uncertainty of heats of fusion, transition, or reaction estimations is 20-50%.

24. Applications of DTA Physical Chemistry Heat of a Reaction Specific Heat of substance like Naphthalene. Thermal Diffusivity of samples Analytical Chemistry Identification of Products since no two products have identical curves. Determination of Melting point.

25. Applications of DTA 1 . To construct phase diagrams and study phase transitions. To find ∆H Peak areas depend upon sample mass, m, enthalpy change ∆H of the process, and geometric and conductivity factors such as heating rate φ and particle size (included in a constant k for a certain substance). Usually the sample peak area is compared with a standard undergoing an enthalpy change at a similar T (since the calibration constant depends on T), under the same conditions, e.g. indium MPt 156.4 C; ∆H fusion = 28.5 J g-1

26. 3. To fingerprint substances 4. To determine M.Pt ., B.Pt ., decomposition temperatures of organic compounds .

27. 5. To characterize inorganic materials The peak at 113°C corresponds to a solid-phase change from the rhombic to the monoclinic form, while the peak at 124°C corresponds to the melting point of the element. Liquid sulphur is known to exist in at least three forms, and the peak at 179°C apparently involves a transition among these. The peak at 446°C corresponds to the boiling point of sulphur .

28. 6. To quantitatively analyze polymer mixtures This is a thermogram of a physical mixture of seven commercial polymers. Each peak corresponds to the characteristic melting point of one of the components. Poly tetrafluoroethylene (PTFE) has an additional low temperature peak, which arises from a crystalline transition. Clearly, differential thermal methods can be useful for qualitative analysis of polymer mixtures.

29. 7. To characterize polymers Schematic DTA thermal curves for the totally amorphous polymer structure and the semi crystalline polymer structure. Both show Tg ; only the semi-crystalline polymer has a crystallization exotherm.

30. Cont… Quantitative analysis of Compounds Determination of Structural and Chemical changes occurring during heat treatments. Quality Control of Cement, glass, textiles, soils, explosives and resins.

31. Differential Scanning Calorimetry

32. Definitions • A calorimeter measures the heat into or out of a sample. • A differential calorimete r measures the heat of a sample relative to a reference. • A differential scanning calorimeter does all of the above and heats the sample with a linear temperature ramp. • Endothermic heat flows into the sample. • Exothermic heat flows out of the sample.

33. • Differential Scanning Calorimetry (DSC) measures the temperatures and heat flows associated with transitions in materials as a function of time and temperature in a controlled atmosphere. • These measurements provide quantitative and qualitative information about physical and chemical changes that involve endothermic or exothermic processes , or changes in heat capacity . DSC: The Technique

34. Conventional DSC Metal 1 Metal 2 Metal 1 Metal 2 Sample Empty Sample Temperature Reference Temperature Temperature Difference = Heat Flow A “linear” heating profile even for isothermal methods

35. Thermal Analysis Differential Scanning Calorimetry (DSC)

36. DSC Cell

37. What can DSC measure? Glass transitions Melting and boiling points Crystallisation time and temperature Percent crystallinity Heats of fusion and reactions Specific heat capacity Oxidative/thermal stability Rate and degree of cure Reaction kinetics Purity

38. DSC Measure Transitions : Glass Transition Temperature (T g ) Melting Temperature (T m ) Crystallization Temperature ( T c )

39. Think First………Heat Later Does the sample contain volatile components? - 2 to 3% water/solvent can lower the glass transition temperature (T g ) by up to 100 o C. - Evaporation creates endothermic peaks in standard (non-hermetic) DSC pans and can be suppressed with use of hermetic DSC pans.

40. 2. At what temperature does the sample decompose? Set the upper limit of the DSC experiment based on decomposition temperature ( TGA ). No meaningful DSC data can be obtained once decomposition results in a 5% weight loss . Decomposition affect: the quality of the baseline due to both endothermic and exothermic heat flow, the quality of the baseline for future experiments and can affect the useful lifetime of the DSC cell due to corrosion.

41. 3. How does thermal history (temperature and time) affect DSC results on my sample? 4. Identical materials can look totally different based on: Storage temperature and time. Cooling rate from a temperature above Tg or above the melting point. Heating rate. Different kinds of experiments may need to be performed in order to measure the current structure vs. comparing samples to see if the materials are the same .

42. Amorphous Structure Glass Transition (T g ) Detectable by DSC due to a step increase in heat capacity as the sample is heated to a temperature above the glass transition temperature (T g ). Important transition because significant changes in physical properties, reactivity and storage stability occur at T g .

43. Glass Transition (T g ) Reporting T g as a single temp., it is necessary to state: What point in the step change (onset, midpoint or end) is being measured. The experimental conditions used to measure T g : heating rate, sample weight.

44. Glass Transition (T g ) To increase sensitivity: Use >10mg samples. Quench cool sample from a temperature above the melt to maximize amorphous structure.

45. T g sensitivity Use >10 o C/min heating rates.

46. Glass Transition (T g ) As a little as 2-3% water can lower T g by up to 100 o C. To measure an accurate T g in a sample with a volatile component by running sample in a hermetic (sealed) pan . Use a dry-box or dry-bag to prepare samples in hermetic pans. This eliminates water absorption during preparation and loss water during the measurement.

47. Crystalline Structure Crystalline structure in a sample is determined from the presence of an endothermic melting peak . Important complimentary techniques to DSC include: Hot Stage Microscopy X-Ray Diffraction (XRD) Nuclear Magnetic Resonance (NMR) Infrared Spectroscopy

48. Crystalline Structure Factors which complicate DSC analysis: Endothermic peaks can be created by evaporation and decomposition as well as melting. TGA should be done on all new samples prior to DSC to determine volatile content and decomposition temperature. Dehydyration / Desolvatio n usually results in loss of crystalline structure. Melting is a thermodynamic transition and therefore, the onset of melting does not change significantly with heating rate. Decomposition is a kinetic (time-dependent) transition and therefore, the onset temperature of the peak shifts to a significantly higher temperature at higher heating rate.

49. 6 DSC Thermogram Temperature Heat Flow - > exothermic Glass Transition Crystallisation Melting Cross - Linking (Cure) Oxidation

50. 79 . 70 °C ( I ) 75 . 41 °C 81 . 80 °C 144 . 72 °C 137 . 58 °C 20 . 30 J / g 245 . 24 °C 228 . 80 °C 22 . 48 J / g Cycle 1 - . 5 . . 5 1 . 1 . 5 Heat Flow ( W / g ) 50 100 150 200 250 300 Temperature ( °C ) Sample : PET 80 PC 20 _ MM 1 1 min Size : 23 . 4300 mg Method : standard dsc heat - cool - heat Comment : 5 / 4 / 06 DSC File : C :... \ DSC \ Melt Mixed 1 \ PET 80 PC 20 _ MM 1 . 001 Operator : SAC Run Date : 05 - Apr - 2006 15 : 34 Instrument : DSC Q 1000 V 9 . 4 Build 287 Exo Down Universal V 4 . 2 E TA Instruments Example DSC - PET T g T c T m

51. 6 70 Influence of Sample Mass Temperature (°C) 150 152 154 156 -2 -4 -6 DSC Heat Flow (W/g) 10mg 4.0mg 15mg 1.7mg 1.0mg 0.6mg Indium at 10°C/minute Normalized Data 158 160 162 164 166 Onset not influenced by mass

52. 6 Effect of Heating Rate on Indium Melting Temperature 154 156 158 160 162 164 166 168 170 - 5 - 4 - 3 - 2 - 1 1 Temperature ( ° C) Heat Flow (W/g) heating rates = 2, 5, 10, 20 ° C/min

53. DSC: Main Sources of Errors Calibration Contamination Sample preparation – how sample is loaded into a pan Residual solvents and moisture. Thermal lag Heating/Cooling rates Sample mass Processing errors

54. Other DSC Techniques Hyper-DSC Based on principle that high heating rates give large broad transitions. Heating rates typically 400-500 o C/min Need very small sample sizes (~nanograms) Good for: A quick overview of new sample Picking out minute transition Poor for: Accuracy: transitions can be shifted by as much as 40 o C Repeatabiliy: Very sensitive to thermal lag.

55. Thermal Analysis Differential Scanning Calorimetry (DSC) DSC is a thermal method of analysis to study the thermal behaviour and thermal properties of materials (typically polymers). The material is sealed in a sample pan and subjected to a controlled temperature programme. The resulting thermograph can yield much valuable information about the properties of the material analysed. Main use of DSC: Material Identification (T m and D H f ) based on IS EN ISO 3146:2000; Method C2

56. Thermal Analysis Differential Scanning Calorimetry (DSC) Other uses of DSC: % Crystallinity determination by DSC (based on IS EN ISO 3146:2000; Method C2). Purity and Polymorphism analysis by DSC. Thermal Stability of materials (e.g. – oxidative induction time (OiT) of materials) by DSC.

57. Thermal Analysis Differential Scanning Calorimetry (DSC)

58. Other DSC Techniques Modulated DSC Composite heating profile: Determines heat capacity and separates heat flow into that due to reversible and non-reversible events. Typicaly: Heating rates: 0 - 5 C Modulation: Period: 60 second Amplitude: +/-1 C

59. Benefits Increased Sensitivity for Detecting Weak (Glass) Transitions Eliminates baseline curvature and drift Increased Resolution Without Loss of Sensitivity Two heating rates (average and instantaneous) Ability to Separate Complex Thermal Events and Transitions Into Their Heat Capacity and Kinetic Components Ability to Measure Heat Capacity (Structure) Changes During Reactions and Under Isothermal Conditions Downside Slow data collection Modulated DSC

60. Example MDSC

61. Technical Group Talk Reversible Transitions Glass Transition Melting Non-reversible Crystallisation Curing Oxidation/degradation Evaporation

62. Aspect DSC DTA 1.Size of Sample 2-10 mg 50-20mg 2. Sensitivity A few joule/mol 0.5kJ/mol 3.Heating & Cooling cycles Programmed Heating & Cooling is possible. Programmed heating 4. Second order phase transition It can be observed with a sample of 200mg It is not observed 5. Specfic heat measurement Accurate Not accurate Comparison of DSC & DTA

63. References Instrumental Methods of Chemical Analysis- By, G.R. Chatwal & S.K. Anand. Instrumental methods of analysis; seventh edition by Willard. Merritt, Dean Seffle . www. wikipedia.com