thermalmethods6586575646543646455543646.ppt
- 1. Thermal Methods of Analysis
- 2. CONTENTS Introduction Types of Different Thermal Analysis TGA Principle Instrumentation Application DTA Principle Instrumentation Application DSC Principle Instrumentation Application Factor affecting to Thermal analysis References
- 3. Introduction • THERMAL ANALYSIS – Techniques in which a physical (thermal) property of a substance is measured as a function of temperature while the substance is subjected to a controlled temperature variation.1 THERMAL ANALYSIS means the analysis of a change in a property of a sample, which is related to an imposed temperature alteration.2
- 4. There is difference between “thermoanalytical techniques” and “thermoanalytical methods”. The techniques are characterized by the suffix “-metry”, while the more comprehensive methods, which include the evaluation and interpretation of the measured property values, are indicated by adding “analysis”. Measurements are usually continuous and the heating rate is often, but not necessarily, linear with time. The results of such measurements are thermal analysis curves and the features of these curves (peaks, discontinuities, changes of slope, etc.) are related to thermal events in the sample.
- 6. When matter is heated, it undergoes ƒ1) Physical Changes:- Phase change such as melting Vaporization, crystallization, transition between crystal structures, change in microstructures in metal alloy & polymers, 2) Chemical Changes:- iclude reaction to form new products, oxidation, decomposition, dehydtation, corrosion
- 7. Types of Different Thermal Analysis Properties Techniques Methods Abbreviations Mass Thermogravimetry Thermogravimetric Analysis TGA Pressure Thermomanometry Thermomanometric Analysis TMA Electric Properties Thermoelectrometry Thermoelectric Analysis TEA Optical Properties Thermooptometry Thermooptometric Analysis TOA Dimensions or Mechanical Properties Thermomechanometry Thermomechanical Analysis TMA Temperature Thermometry Heating & Cooling Curve Analysis -- Temperature Difference Differential Thermometry Differential Thermal Analysis DTA Heat flow Difference Differential Scanning Calorimetry -- DSC
- 8. Thermogravimetric Analysis (TGA) Principle:- The mass of a sample in a controlled atmosphere is recorded continuously as a function of temperature or time as the temperature of the sample is increased (usually linearly with time). Measurements of changes in sample mass with temperature. The temperature is increased at constant rate for known initial weight of substance & change in weight are recorded as function of temperature at different interval of time. Note that mass is a measure of the amount of matter in a sample, whereas weight refers to the effect of the gravitational force on a mass. A plot of mass or mass percentage as a function of time is called a thermogram or a thermal decomposition curve.
- 9. Instrumentation 1. Thermobalance 2. Furnace 3. Sample Holder 4. Temperature measurement 5. Computer-Data acquisition , processing & control system
- 10. Thermobalance The usual range of thermobalance, is from 1 to 1000 mg, with usual sample weighing between 5 to 20 mg. It provide electronic signal to record the change in mass. Types of Thermobalance 1) Null Point type balance 2) Deflection type balance
- 11. various position of balance in furnace
- 12. furnace Furnaces for TGA cover the range from ambient temperature to l000°C,although some can be used for temperatures up to 1600°C. Heating rates can often be selected from 0.1°C/min to 100°C/min. Some units can heat as rapidly as 200°C/min. Insulation and cooling of the exterior of the furnace is required to avoid heat transfer to the balance. Nitrogen or argon is usually used to purge the furnace and prevent oxidation of the sample.
- 13. Sample Holder Samples are typically contained in sample pans made of platinum, aluminum, or alumina. Platinum is most often used because of its inertness and ease of cleaning.
- 14. Temperature measurement Thermocouple- Wires- Platinum, Rhodium, Chromium, Nickel Resistance Thermometers- The electrical resistances of metallic conductors increase with rising temperature
- 15. TG Curve Type (i) curves: The sample undergoes no decomposition with loss of volatile products over the temperature range shown. Type (ii) curves: The rapid initial mass-loss observed is characteristic of desorption or drying. Type (iii) curves: represent decomposition of the sample in a single stage. Type (iv) curves: indicate multi-stage decomposition with relatively stable intermediates. Type (v) curves: represent multi-stage decomposition, but in this example stable intermediates are not formed. Type (vi) curves: show a gain in mass as a result of reaction of the sample with the surrounding atmosphere. Type (vii) curves: are not often encountered. The product of an oxidation reaction decomposes again at higher temperatures
- 16. Applications • Determination of purity & thermal stability of primary & secondary standards. • Determination of composition of complex mixture & decomposition • For study of sublimation behavior of compound • To study reaction kinetics • Determination of Dehydration / Desolvation
- 17. Differential Thermal Analysis Principle:- Differential thermal analysis (DTA) is a technique in which the difference in temperature between a substance and a reference material is measured as a function of temperature while the substance and reference material are subjected to a controlled temperature program. The differential temperature is plotted against temperature or time is called DTA curve. Both sample & reference material heated in controlled condition. If any reaction (physical or Chemical changes ) takes place temperature difference (∆T) will occur between sample & reference material.
- 18. reference material The reference material should have the following characteristics: (i) It should undergo no thermal events over the operating temperature range. (ii) It should not react with the sample holder or thermocouple, (iii) Both the thermal conductivity and the heat capacity of the reference should be similar to those of the sample. For inorganic samples- Alumina, and carborundum, SiC, For organic compounds- octyl phthalate and silicone oil.
- 19. INSTRUMENTATION 1. Furnace 2. Sample Holder 3. Temperature measurement 4. Computer-Data acquisition , processing & control system
- 20. Furnace Both sample & reference material match thermally & arranged systematically with the furnace, so that both are heated or cooled in identical manner. The metal block surrounding the well act as heat sink. Temperature of the heat sink slowly increases by using internal heater. Its temperature range from ambient temperature to l600°C
- 21. Sample Holders Sample holder called crucible are made up of metallic (Aluminum , Platinum) & ceramic (silica). Sample are usually 1- 10 mg for analysis. The dimension of two crucibles & cell well are as nearly identical as possible.
- 22. Temperature measurement Pair of thermocouples used in DTA.
- 23. DTA CURVE The initial decrease in T is due to the glass transition. The glass transition temperature Tg is the characteristic temperature at which glassy amorphous polymers become flexible or rubberlike. The two maxima are the result of exothermic processes in which heat is evolved from the sample, thus causing its temperature to rise. When heated to a characteristic temperature, many amorphous polymers begin to crystallize as microcrystals, giving off heat in the process. Crystal formation is responsible for the first exothermic peak The minimum labeled "melting" is the result ofan endothermic process in which heat is absorbed by the analyte. The second peak in the figure is endothermic and involves melting of the microcrystals formed in thc initial exothermic process. The third peak is exothermic and is encountered only if the heating is performed in the presence of air or oxygen. The final negative change in ∆T results from the endothermic decomposition of the polymer to produce a variety of products.
- 24. Applications DTA is a widely used tool for studying and characterizing polymers. The types of physical and chemical changes in polymeric materials that can be studied by DTA. DTA is also used in the ceramics and metals industry. DTA is used to study decomposition temperatures, phase transitions, melting and crystallization points, and thermal stability. An important use of DTA is for the generation of phase diagrams and the study of phase transitions. The DTA method also provides a simple and accurate way of determining the melting, boiling, and decomposition points of organic compounds.
- 25. Differential Scanning Calorimetry Principle:- Differential Scanning Calorimetry (DSC) is a Thermal Analysis technique in which the heat flow rate (power) to the sample is monitored against time or temperature while the temperature of the sample, in a specified atmosphere, is programmed. It is measure heat into or out of sample. Differences in heat flow occur with the occurrence of two major events- 1) The heat capacity of the sample which increses with temperature 2) Transitions occur
- 26. Instrumentation 1. Furnace 2. Sample Holder 3. Temperature measurement 4. Computer-Data acquisition , processing & control system
- 27. Instrumentation Types of DSC 1) Power-compensated DSC 2) Heat-flux DSC 3) Modulated DSC
- 28. power-compensated DSC In power-compensated DSC, the temperatures of the sample and reference are kept equal to each other while both temperatures are increased or decreased linearly. The power needed to maintain the sample temperature equal to the reference temperature is measured.
- 29. heat-flux DSC In heat-flux DSC, the difference in heat flow into the sample and reference is measured while the sample temperature is changed at a constant rate. Both sample and reference are heated by a single heating unit.
- 30. Modulated DSC Modulated DSC (MDSC) uses the same heating and cell arrangement as the heat-flux DSC method. In MDSC, a sinusoidal function is superimposed on the overall temperature program to produce a micro heating and cooling cycle as the overall temperature is steadily increased or decreased.
- 31. Dsc CURVE
- 32. applications Glass Transition Temperatures :- Determination of the glass transition temperature T, is one of the most important applications of DSC. The physical properties of a polymer undergo dramatic changes at Tg, where the material goes from a glassy to a rubbery state. At the glass transition, the polymer undergoes changes in volume and expansion, heat flow and heat capacity. The change in heat capacity is readily measured by DSC. Crystallinity and Crystallization Rate:- In most cases DSC is one of the easiest methods for determining levels of crystallinity. Reaction Kinetics:- Many chemical reactions, such as polymer formation reactions, are exothermic and readily monitored by DSC methods.
- 33. Factor affecting to Thermal analysis Instrumental 1) Furnace Heating rate- es heating rate , es decomposition ↑ ↑ 2) Furnace atmosphere- pure intert gas like N2 Sample characteristics 1) Sample particle size 2) Weight of sample
- 34. References 1. Douglas A. Skoog, Principles of Instrumental Analysis, 6th Edition, 894-904. 2. Michael E. Brown ,Introduction to Thermal Analysis Techniques and Applications, 2nd Edition. 3. Gurdeep Chatwal , Instrumental methods of chemical analysis : Analytical Chemistry.
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